Flue Gas Conditions Research Articles

Self-template synthesis of Co3O4 nanotube for efficient Hg0 removal from flue gas

The adsorption of elemental mercury (Hg0) is a widely used technology to remove Hg0 from flue gas. The morphology and structure of sorbents, which have serious impacts on the number and availability of adsorption sites and the mass transfer of Hg0, play an important role in Hg0 removal process. Nanotube materials have through-pore structures leading to lower mass transfer resistance and more adsorption sites for Hg0. Given this, organic–inorganic hybrid nanowires were prepared by hydrothermal method as self-template. After calcination with a controlling heating rate and temperature, a series mesoporous Co3O4 nanotube sorbents were obtained. Characterization results show that the heating rate mainly affects the pore structure of the sorbents, while the calcination temperature mainly affects the surface morphology. When the calcination temperature is 400 °C and the calcination rate is 0.5 °C /min, the sorbent (Co3O4-T400-R0.5) has a clear 1D tubular structure which can effectively reduce the mass transfer resistance. And the unique internal surface of the tubular structure can provide more active sites, which can effectively avoid the competitive adsorption of Hg0 and other gas components. Furthermore, Co3O4-T400-R0.5 has the highest Co3+/Co2+ ratio leading to a better redox property, which is of benefit to Hg0 removal process. Therefore, the Hg0 removal efficiency of Co3O4-T400-R0.5 can reach more than 90% with a high gas hourly space velocity of 90,000 h− 1 and 0.02 g loading amount at 250 °C. Furthermore, Co3O4-T400-R0.5 has excellent Hg0 removal efficiencies in different flue gas condition showing a high stability.

Formula: see text] modified AC for removing gaseous elemental mercury from flue gas.

Mercury pollution from coal-fired power plants has always been an environmental concern, and adsorption technology is an effective method for Hg0 removal. In this study, copper-iron binary metal sulfide modified activated carbon ([Formula: see text]) adsorbent was synthesized. The performance and mechanism of mercury removal were tested by adsorption experiments and characterization methods. The results showed that the mercury removal efficiency of [Formula: see text] under simulated flue gas (SFG) conditions at 150°C could reach 91%, which was higher than [Formula: see text] and [Formula: see text]. Compared with [Formula: see text], the introduction of Fe increased the proportion of [Formula: see text], which was usually linked to [Formula: see text], resulting in the generation of more [Formula: see text](CuISI) species. Meanwhile, the generation of active sulfur sites such as [Formula: see text] was generated, which had a facilitative effect on the oxidation of Hg0. Stable [Formula: see text] was the predominant product on the adsorbent surface. The 2% sulfur loadings had significantly improved the sulfur resistance of conventional AC.

Assessing the dry impinger method for condensable particulate matter from ultra-low emission coal-fired power plant measurement

The dry impinger method is commonly used for the determination of condensable particulate matter (CPM) emissions. The coil and chamber condenser is used to build different dry impinger methods for CPM sampling. The comparative analysis of coil and chamber condenser is performed in a laboratory experiment to evaluate the deviation caused by SO2. Results showed that the positive deviation caused by SO2 in the chamber condenser is lower than that in the coil condenser under the same sampling conditions, especially under high humidity flue gas. The CPM emission characteristics from Hanchuan coal-fired power plant (CFPP) determined by both dry impinger methods are also investigated as well. The CPM and its most water-soluble ions (e.g., F−, Cl−, NO3−, SO42−, Na+, Ca2+ and NH4+) measured by method #2 (chamber condenser) are higher than that of method #1 (coil condenser). In addition, the esters in the CPM also increased with the CPM concentrations. Based on above evidences, it can be inferred that the dry impinger method with chamber condenser, will be recommended as the appropriate method for measuring CPM emitted from stationary sources, especially under the high humidity flue gas conditions.

Self-activated, urea modified microporous carbon cryogels for high-performance CO2 capture and separation

Conventionally, porous carbons were synthesized using corrosive chemical activating agents. On contrary, we designed a single-step synthesis method for the preparation of a series of self-activated heteroatom (N)-doped carbon cryogels from potassium hydrogen phthalate (KHP) and urea at various temperatures (700–1000 °C), in the absence of any activating agent. To highlight the effectiveness of N-doping in porosity generation and CO2 adsorption/separation, a comparative analysis was drawn with a series of undoped carbon cryogels. Notably, the N-doped cryogels exhibit a highly porous structure with remarkable specific surface area (SSA; 2084 m2 g−1), micropore volume (1.1806 cm3 g−1), well-defined pore size distribution, and abundant narrow micropores (<1.04 nm). Additionally, a considerable mechanical strength (compressive strength = 0.621 MPa and compressive modulus = 8.86 MPa) was also observed. Moreover, the porous cryogel endowed with sufficient pyrrolic nitrogen content (≈51.4 at %) lead to high CO2 adsorption (280.57 mg/g at 273 K and 171.31 mg/g at 298 K at 1 bar) and an excellent ideal adsorbed solution theory (IAST)-based CO2/N2 selectivity (≈115) at 273 K, surpassing the CO2 adsorption/separation performance of previously reported N-doped carbons and resorcinol-based carbon gels. Furthermore, the moderate heat of adsorption (36.109 kJ mol−1) and stable cyclic behavior of CO2 adsorption-desorption under flue gas conditions (i.e., 15% CO2/85% N2) unveils the physisorption nature of adsorption which governs the energy-effective regeneration process. Summarizing, the present work demonstrates the successful fabrication of highly porous carbon cryogels as efficient CO2 adsorbents, thereby opening new synthetic avenues for self-activating porous carbon formation.

Experimental Study on the Kinetics of CO2 and H2O Adsorption on Honeycomb Carbon Monoliths under Cement Flue Gas Conditions.

The main challenge of adsorption consists in the production of materials that can be used in real situations. This study comprehensively describes the CO2 and H2O adsorption behavior of honeycomb-shaped sorbents commonly used in rapid pressure swing adsorption cycles (RPSA). With this purpose, the kinetics and equilibrium of adsorption of CO2/H2O/N2 mixtures on three honeycomb carbon monoliths (793, 932, and AM03) were assessed in a thermogravimetric analyzer (TGA) under different postcombustion capture scenarios (temperature of 50 °C and several concentrations of CO2). The kinetics study exhibited that the single adsorption of CO2 and H2O can be adequately described by the Avrami and exponential decay-2 models, respectively. As expected, the three carbon monoliths presented fast adsorption of CO2 from a CO2/H2O mixture. Furthermore, when humid flue gas was considered, overall adsorption kinetics were governed by CO2. Besides, the experimental data fitting to the intraparticle diffusion model showed that gradual CO2 and H2O diffusion toward the micropores was the rate-limiting stage. The obtained results give a better insight into the selective adsorption of CO2 and the potential of honeycomb carbon monoliths to separate CO2 from humid flue gas in the context of the cement industry. Carbon monolith 793 is the best carbon monolith candidate to capture CO2 under the evaluated conditions: a capacity of adsorption of 1 mmol of CO2 g–1 and favorable kinetics in 32 vol % CO2 and 4 vol % H2O(v), at 50 °C and 101.3 kPa.

Zeolitic imidazolate frameworks with different organic ligands as carriers for Carbonic anhydrase immobilization to promote the absorption of CO2 into tertiary amine solution

Carbonic anhydrase (CA) enzyme-based absorption processes represent a promising approach to flue gas CO2 capture owing to their rapid absorption rates and low energy penalties. However, CA enzymes exhibit poor stability and activity under typical flue gas conditions, thus constraining their industrial utilization. Enzyme immobilization has been proposed as a potential means of improving associated stability and activity levels, thus overcoming these limitations. Herein, a variety of zeolitic imidazolate frameworks including ZIF-8, ZIF-11, and ZIF-90 with a range of organic ligands were synthesized as adsorption-based carriers for CA enzyme immobilization. In a series of experiments, CA immobilized on ZIF-8 (CA/ZIF-8) was found to retain higher activity levels that were approximately 86% of those of the free enzyme, as compared to 44% and 16% for CA/ZIF-11 and CA/ZIF-90, respectively. Immobilized CA and associated carrier frameworks were characterized via XRD, SEM, and BET. Variations in CA enzyme secondary structural characteristics in the context of immobilization were monitored via FTIR and CD to explore the molecular basis for variable activity levels associated with different carriers, revealing more hydrophilic materials to be conducive to the preservation of enzymatic activity. In addition, carrier precursor selection should take both hydrophilicity and the potential inhibitory effects of functional groups on the CA enzyme into account.

Investigation of low-temperature NO2 reduction by NH3 over activated carbon: Effect of pore structure and flue gas conditions

NO2–NH3 selective catalytic reduction (SCR) over activated carbon (AC) is a potential deNOx method at low temperatures. In this study, a series of AC samples with developed pore structures were prepared through CO2 activation. DeNOx activity tests indicated that the increase in specific surface area enhanced NOx conversion and decreased the temperature corresponding to the highest NOx conversion. FGAC900, which had the highest specific surface area, showed the highest NOx conversion of 97.80% at 150 °C. The influence of various flue gas conditions was also investigated. O2 concentrations in the range of 0–20 vol% had little effect on NOx conversion. The appropriate gas hourly space velocity and NH3 concentration are important for achieving superior deNOx performance. When 8 vol% H2O was added into dry simulated flue gas at 150 °C, NOx conversion decreased from 97.80% to 90.71%. Transient response experiments and density functional theoretical calculation results showed that the inhibition of H2O is reversible and results from competitive physisorption between NO2 and H2O molecules. The in situ DRIFT results indicated that NH4NO3 is an important intermediate. An efficient deNOx AC catalyst with a developed pore structure was prepared, and the effects of flue gas conditions were systematically investigated.

Carbon Dioxide Capture Chemistry of Amino Acid Functionalized Metal-Organic Frameworks in Humid Flue Gas.

Metal-organic framework-808 has been functionalized with 11 amino acids (AA) to produce a series of MOF-808-AA structures. The adsorption of CO2 under flue gas conditions revealed that glycine- and dl-lysine-functionalized MOF-808 (MOF-808-Gly and -dl-Lys) have the highest uptake capacities. Enhanced CO2 capture performance in the presence of water was observed and studied by using single-component sorption isotherms, CO2/H2O binary isotherm, and dynamic breakthrough measurements. The key to the favorable performance was uncovered by deciphering the mechanism of CO2 capture in the pores and attributed to the formation of bicarbonate as evidenced by 13C and 15N solid-state nuclear magnetic resonance spectroscopy studies. On the basis of these results, we examined the performance of MOF-808-Gly in simulated coal flue gas conditions and found that it is possible to capture and release CO2 by vacuum swing adsorption. MOF-808-Gly was cycled at least 80 times with full retention of performance. This study significantly advances our understanding of CO2 chemistry in MOFs by revealing how strongly bound amine moieties to the MOF backbone create the chemistry and environment within the pores, leading to the binding and release of CO2 under mild conditions without application of heat.

Experimental study and reaction mechanism on the process of Br addition for mercury emission control

Application of halogen additive (CaCl2, CaBr2) has recently been shown to decrease Hg0 concentration significantly in the hazardous waste incineration flue gas. However, the reaction mechanism of Hg0 oxide active substance has currently not yet been studied. In this paper, the effect of CaBr2 on Hg0 oxidation under different combustion conditions and the reaction mechanism of effective reaction components (bromine free radicals) detected by the EPR (Electron Paramagnetic Resonance) method are studied. For the first time, the correlation between bromine radical and Hg0 oxidation is shown, which eventually affects the transformation path of Hg0 in the flue gas. Under different working conditions, the oxidation effect of CaBr2 solution additives on Hg0 in flue gas has been verified in the experiment platform. CaBr2 can still effectively oxidize Hg0 in complex flue gas conditions of the hazardous waste incineration plant. These results provide a new fundamental understanding of the oxidation path of Hg0 under the influence of bromine free radicals and show that spraying calcium bromide solution is an effective means to avoid atmospheric Hg0 emissions, contributing to its global distribution in a significant way.

A scalable metal-organic framework as a durable physisorbent for carbon dioxide capture.

Metal-organic frameworks (MOFs) as solid sorbents for carbon dioxide (CO2) capture face the challenge of merging efficient capture with economical regeneration in a durable, scalable material. Zinc-based Calgary Framework 20 (CALF-20) physisorbs CO2 with high capacity but is also selective over water. Competitive separations on structured CALF-20 show not just preferential CO2 physisorption below 40% relative humidity but also suppression of water sorption by CO2, which was corroborated by computational modeling. CALF-20 has a low enthalpic regeneration penalty and shows durability to steam (>450,000 cycles) and wet acid gases. It can be prepared in one step, formed as composite materials, and its synthesis can be scaled to multikilogram batches.

Development and testing of a new post-combustion CO2 capture solvent in pilot and demonstration plant

Post-combustion CO2 capture for coal-fired power plants is an important technical option to mitigate greenhouse gas emission from coal-based power generation. CO2 capture based on chemical absorption is currently the dominant technology for large-scale capture unit. The main obstacle of commercial application is the high cost and high energy consumption, innovation of new absorption solvent is one of the keys to the performance improvement. Based on the characteristics of flue gas, combined with the analysis and comparison of potential amine components, the formula of blended amines are developed, which is further screened by true-heat flux calorimetric test combined with vapor-liquid equilibrium test, HNC-5 is selected through the lab test, because of its lower heat of absorption and higher capture performance. The test on a 1000 t/a CO2 capture pilot plant under real flue gas conditions shows that the performance index of HNC-5 is consistent with the lab test results. The CO2 capture ratio is higher than 90%, and the heat consumption during regeneration is reduced by about 20% compared with MEA. The continuous operation results of the 120,000-ton/year CO2 capture unit show that heat duty of regeneration of HNC-5 is about 2.8GJ/tCO2, the cost per ton of CO2 captured is reduced by about 63 CNY, the usage life is longer, helping improve the system availability and reliability.

Carbonation of High-Ca Fly Ashes under Flue Gas Conditions: Implications for Their Valorization in the Construction Industry

The utilization of high-calcium fly ashes (HCFA) from coal-fired power plants in the construction industry is problematic, since their high free lime contents can lead to durability problems. In this research, the carbonation of a high-CaO fly ash has been carried out using simulated flue gas and concentrated CO2, with the aim to assess the valorization potential of such materials in the construction industry. The results show that, at 7 bars total pressure, an up to 36% carbonation efficiency can be achieved in just 30 min when pure CO2 is used; a comparable result with flue gas requires about 4 h of reaction. On the other hand, experiments carried out at atmospheric pressure show significantly different carbonation efficiencies depending on the CO2 concentration of the gas used. All experiments resulted in a substantial reduction in the original free lime content, and after reaction times of 4 h (at atmospheric pressure) and pressures of 7 bars (for any reaction time &gt;30 min), the final free lime values were low enough to comply with the requirements of European Standards for their utilization as additions in cement.

Arsenic adsorption enhancement performances of Mn-modified γ-Al2O3 with flue gas constituents involved

Some flue gas constituents have negative effects on As2O3 adsorption of γ-Al2O3 so promoting arsenic adsorption performances under complicated flue gas conditions is necessary based on previous studies. In this study, γ-Al2O3 is modified with manganous nitrate and then Mn-modified γ-Al2O3 is used as the adsorbents in experiments. Besides, molecular dynamics (MD) simulations and density functional theory (DFT) calculations are performed to explore mechanisms of how loadings of Mn enhance arsenic adsorption features of γ-Al2O3 when being affected by flue gas constituents in microscale and mesoscale, respectively. As for DFT calculations, it is uncovered that electron transfer/interaction among As2O3, flue gas constituents and Mn-modified γ-Al2O3 mostly influences arsenic adsorption. For MD simulations, it is expounded that the collision and aggregation of As2O3 and flue gas constituent molecules have most impact on arsenic adsorption. As far as experiments are concerned, they are conducted to show the macroscopic characterizations of arsenic adsorption performances, corresponding to results of DFT calculations and MD simulations. The understanding of these three different aspects could supply significant references for utilization of Mn-modified γ-Al2O3 in real industries to remove arsenic under complex flue gas conditions.

Mass transfer coefficients of carbon dioxide in aqueous blends of monoethanolamine and glycerol using wetted-wall column

There is an urgent need for CO2 capture development because of the global warming crisis. Recently CO2 absorption by the mixture of monoethanolamine (MEA) and glycerol, as an eco-friendly solvent, has been considered due to its promising performance and low technical and environmental impacts. However, more aspects of this process, especially mass transfer coefficients, need to be studied further. In this work, a bench-scale wetted-wall column was used to find the CO2 mass transfer coefficients in the aqueous blends of MEA (25 wt%) and glycerol (5–20 wt%). The experiments were performed nearly to the industrial conditions of flue gas at atmospheric pressure and three different temperatures (313, 323, and 333 K). The gas flow rate was maintained around 0.17 ± 0.01 stdL/s, and the CO2 partial pressure was in the range of 1–15 kPa. The findings revealed that increasing the glycerol to 10 wt% improves the overall mass transfer (KG), and adding more glycerol up to 20 wt% decreases the KG. The gas-side mass transfer resistance (1/kg) found to be negligible. Thus, the primary mass transfer resistance was in the liquid phase. It is also found that the solution with 10 wt% glycerol and 25 wt% MEA (10G25M) had the highest liquid-side mass transfer coefficient (kg′) among the other solutions. The 10G25M showed a comparable and even better absorption rate than solutions with a higher concentration of MEA studied in the literature. Compared with industrial-grade, the kg′ of the 10G25M was over two times higher than the 30 wt% MEA solution.

Efficient micropore sizes for carbon dioxide physisorption of pine cone-based carbonaceous materials at different temperatures

Biomass-based activated carbons (ACs) are widely used as CO2 capturing materials. Most plant-based biomass contains a phytolith component that mainly comprises silica, which is an obstacle for developing the porosity of ACs. The silica elimination process (SE) has rarely been studied for developing the porosity of ACs. Here, we prepared pre-carbonized pine cones (CPC) as a starting material to investigate optimizing the micropores of ACs according to the preparation sequence. One was prepared by chemical activation (CA) and the subsequent SE (CPC-CA-SE/ACs) and the other was carried out the SE before CA (CPC-SE-CA/ACs). It was found significant differences on the pore development between two samples, the former showed a specific surface area of 1787 m2 g−1 and the microporosity of ∼92 % while the latter were 2047 m2 g−1 and ∼74 %, respectively. The highest CO2 adsorption capacities were exhibited in CPC-CA-SE/ACs of 6.57 mmol g−1 at 273 K and 1 bar, resulting from the effective pore size (< 1.1 nm). Furthermore, the highest CO2 capture performance of 0.75 mmol g−1 in the typical flue gas condition (15 % CO2/85 % N2) and superior regeneration properties during 10 adsorption–desorption cycles at 313 K were achieved in CPC-CA-SE/ACs. From the results, we found that the preparation sequence had a strong effect on the textural properties of the resultant of biomass-based ACs and their CO2 capture performance.

Valorization of shrimp shell biowaste for environmental remediation: Efficient contender for CO2 adsorption and separation

Over the years, single heteroatom-doped biowaste-derived activated carbons were studied for effective CO2 adsorption. However, binary or ternary heteroatoms-doping is equally important and could significantly affect the CO2 adsorption and flue gas (i.e., CO2/N2) separation. Herein, for the first time, shrimp shell-derived chitosan was used to design a series of ternary (N, S, O)-doped hierarchically porous carbons. The resultant carbons exhibit a large specific surface area (up to 2095 m2/g), micropore volume (up to 1.2647 cm3/g), and high heteroatoms content i.e., N up to 4.1 at. %, S up to 4.6 at. %, and O up to 13.4 at. %. Consequently, high CO2 uptake of 236.80 mg/g at 273 K/1 bar and an excellent CO2/N2 gas selectivity (84.3) was observed, attributed to the synergistic role of narrow micropores (<1 nm) and optimum heteroatom content. Furthermore, the stable CO2 adsorption-desorption cyclic behavior under flue gas conditions i.e., 15% CO2/85% N2 reveals the physisorption mechanism of CO2 adsorption and appears to be an energy-efficient regeneration process. Concluding, our work demonstrates a facile route of valorization of biowaste for environmental remediation to combat biowaste accumulation and mitigating atmospheric CO2 levels, simultaneously.

Pyrolysis of sulfonic acid substituted benzenes and investigation of CO2 capture capability of resulting carbons

Aromatic organic compounds5-sulfosalicylic acid (SSA) and p-toluenesulfonic acid (TsOH) were used to prepare sulfur doped ultramicropore (pores smaller than 0.7 ​nm) containing carbons by pyrolysis under Argon atmosphere. SSA derived carbon processed at 1000 ​°C showed the best CO2 (carbon dioxide) adsorption performance. CO2 sorption capacity of SSA1000 is 3.91 ​mmol g-1at 1 ​bar at 273 ​K and 2.88 ​mmol g-1at 1 ​bar at 298 ​K. Remarkably, at typical flue gas conditions (0.15 ​bar@298 ​K) SSA1000 takes up 0.95 ​mmol ​g-1 CO2. SSA1000 possessed good gas sorption properties, recyclability for regeneration, and Ideal Adsorbed Solution Theory (IAST)-based selectivity of 14.7 (1 ​bar, CO2/N2:0.15/0.85). This work shows the possibility of production of ultramicropore containing sulfur and oxygen doped carbons exhibiting high CO2 uptake capability via simple pyrolysis method from molecular precursors.

A kinetic study of Hg(0) oxidation over Mo-promoted V-based SCR catalyst

A kinetic study of elemental mercury (Hg(0)) oxidation reaction over molybdenum (Mo)-promoted vanadium (V)-based selective catalytic reduction (SCR) catalyst was carried out. To probe the role of HCl and O2 in Hg(0) oxidation over the catalyst, a real-time Hg(0) oxidation experiment was conducted. It was found that Hg(0) adsorption was negligible and HCl adsorbed onto the catalyst surface could show consistent Hg(0) oxidation performances in the presence of O2 at realistic SCR temperatures. NH3 showed competitive adsorption with HCl, resulting in degrading Hg(0) oxidation performance. X-ray Absorption Near-Edge Structure (XANES) data for mercury species showed that HgCl2 was the major mercury species formed onto the spent catalyst under typical flue gas conditions. Based on the current and previous studies, an Eley-Rideal followed by Langmuir-Hinshelwood mechanism was proposed, comprising multiple elementary reaction steps. A steady-state kinetic study was conducted based on an assumption of HgCl formation as a rate-determining step. The kinetic and thermodynamic parameters determined from this study shed light on fundamental insights and practical catalytic reactor designs.

Nonferrous metal flue gas purification based on high-temperature electrostatic precipitation

The removal of fly ash from nonferrous metals industry at high temperatures in electrostatic precipitators (ESPs) has attracted wide attention in reducing the industrial pollution. In this study, the removal characteristics of copper smelting (ash A) and nickel smelting fly ash (ash B) under regular and circulating flue gas conditions were investigated through a high-temperature wire-plate ESP. The two kinds of ash have various resistivity ranges at different temperatures, resulting in better removal of ash B than ash A at relatively low temperatures, whereas the opposite result was obtained at 573 K and 673 K. Besides, under the circulating flue gas condition, the number percentage of large particles was decreased while small particles ascended as the increase of the residence time. After sufficient residence time, the particle mass concentration would reach a stable value under 10 mg/m3. Furthermore, the removal characteristics of the two ash under the barbed electrode (DE2) compared with the round rod electrode (DE1) was also conducted. Results indicated DE2 owned a higher removal efficiency for both ash at high temperature no matter under which condition. Combining the electrode optimization by DE2 and the action of circulating flue gas, the ultimate collection efficiency of ash A and ash B could reach 95.65 % and 95.12 % at 673 K.

Study the thermal radiation effects in gas-solid flows with gray and non-gray P1 models implemented in MFiX

Thermal radiation is a dominant mode of heat transfer in combustion/gasification, packed/circulating bed reactors, and energy storage/conversion devices. In hydrocarbon fuel combustion, the high absorption and emission of product gases like CO2 and H2O significantly affect the heat transfer characteristics. It is essential to understand the radiative energy propagation in such applications. In the present study, we developed a framework to implement the P-1 radiation model in MFiX for Eulerian-Eulerian (Two fluid-TFM) and Eulerian-Lagrangian (Discrete element-DEM and Particle in cell-PIC) models. The P-1 is a simplification of the spherical harmonics method. The framework has been verified on various flue gas conditions. The verified solver results are validated against the benchmark results available in the literature. The verified and validated gray and non-gray weighted sum of gray gas models is evaluated for dry and wet flue gas conditions. They are also used to study gas-solid flows in a fluidized bed/riser.