Abstract: The nitrogen oxides (NOx) produced by the high-temperature combustion of coal in coal-fired power plants cause serious pollution to the environment, and the control of NOx pollutant emission has become a common action around the world. The char-NO heterogeneous reduction reaction that occurs in the reburning zone of the boiler is common during coal combustion process. However, because of the complex chemical structure and composition of char as well as the gas-solid composition in the combustion reaction, the mechanism of the char-NO heterogeneous reduction reaction is not yet clear. In this paper, the research on the char-NO heterogeneous reduction reaction by the density functional theory was summarized. The mechanism of the char-NO reaction was reviewed based on the char model, NO adsorption methods, reaction pathways and the different intermediates produced in reaction pathways. The influence mechanism of CO and minerals on NO heterogeneous reduction was also analyzed. It is pointed out that the oxygen groups and active sites on the edge of the char model are beneficial to NO reduction reaction. The intermediates such as HCN, N2O and NH3 are produced by different reaction pathways. CO and catalytic metals can promote the char-NO reaction by increasing the reactive sites, reducing the reaction energy barrier and increasing the reaction rate, which provides a theoretical basis for the improvement of NO heterogeneous reduction reaction mechanism and the control of NOx emission.
Abstract: Rapid pyrolysis experiment of Zhundong coal was conducted in a high-frequency furnace to investigate release characteristics of alkali and alkaline earth metals (AAEMs) and its correlation with changes of physical and chemical properties of char. Residence time and atmosphere during pyrolysis were important process parameters that affected the migration characteristics of AAEMs and physicochemical structural evolution of char. Experimental results show that the release of AAEMs in coal char increases over time. The maximum release rate of Na, Mg and Ca is 61.05%, 64.47%, and 44.01%, respectively. Promoting effect of CO2 on release of Na mainly occurs in the initial stage of rapid pyrolysis, nevertheless the promoting effect on release of Mg and Ca mainly is in the middle and late stage. CO2 accelerates release of AAEMs by promoting release of volatiles, facilitating decomposition of oxygen-containing functional groups and aliphatic functional groups, and promoting formation of cracks on surface of coal char.
Abstract: A 600 MW circulating fluidized bed boiler power plant and a 1000 MW pulverized coal boiler power plant were selected to study mercury migration, transformation and emission characteristics. The mercury concentration in flue gas was sampled by EPA 30B method, and the solid and liquid samples such as furnace-incoming coal, fly ash, bottom slag, limestone, process water, desulfurization gypsum and desulfurization wastewater were collected for analysis. The synergetic effect of existing pollutant control devices on mercury removal in two power plants was studied, and the migration and transformation law of mercury was discussed. After the flue gas of the two power plants passes through APCDs, the total mercury removal rate reaches over 88%, and the final mercury concentrations of the flue gas are 1.85 and 1.10 μg/m3, which are far lower than the national requirements. Under the existing equipment conditions, the ultra-low mercury emission can be realized.
Abstract: Sludge incineration technology has significant advantages such as capacity reduction and energy utilization, but it will cause heavy metal pollution. Therefore, the co-combustion of dewatered sludge with corn straw at 700−850 ℃ was studied in a laboratory scale internal circulating fluidized bed. The effects of different temperature, sludge mixing ratio and secondary air ratio on the NO emission and the migration of different heavy metals in bottom ash, fly ash and flue gas after co-combustion were examined. The results show that under the experimental conditions, with the increase in temperature, the NO emission concentration increases, and the concentrations of V, Cr, As, Sb and Hg first increase and then decrease in the bottom ash, while the concentrations of Zn, Cu, Se and Cd vary to the contrary. The turning point of most heavy metals concentration is at 800 ℃. However, with the increase in the sludge mixing ratio, the NO emission concentration first decreases and then increases, and the Cu, Hg and Tl concentrations all increase first and then decrease in the bottom ash, while the Cr concentration change is the opposite, with turning points all at the sludge mixing ratio of 10%. Also, with the increase in the secondary air ratio, the NO emission concentration decreases, and the Zn, Cu, Se and Hg concentrations in bottom ash decrease, on the contrary, the As and Cd concentrations increase.
Abstract: Aiming at the head of a 435 m2 sintering machine, the research on the removal characteristics of chemical agglomeration strengthening of fine particles and heavy metals (As, Cr, Cd, Ni, Cu, Pb, Zn, etc.) was carried out by installing chemical agglomeration enhanced dust removal system in front of ESP. The test results show that after chemical agglomeration, the mass concentration of PM10, PM2.5, PM1 particles in the flue gas after the ESP is reduced by more than 49%, the average particle size of fly ash is increased by more than 46%, and the fine particles remove efficiency of ESP is promoted. After chemical agglomeration, the mass concentrations of seven heavy metals in fine particulate matter and fly ash increase, and the mass concentrations of gaseous heavy metals in the flue gas after the ESP decrease. It shows that agglomeration promotes the migration of gaseous heavy metals into fly ash particles, promotes the agglomeration and growth of fine particulate heavy metals. Chemical agglomeration can not only enhance the removal of fine particles, but also effectively improve the removal efficiency of heavy metals.
Abstract: Polyvinyl alcohol (PVA), bacterial cellulose (BC) and sulfuric acid were used as raw materials to prepare PVA/BC composite hydrogel electrolyte (CHEPVA/BC) by physical cross-linking freezing-thawing cycle method. After freeze-thaw cycles, PVA and BC form a large number of intermolecular hydrogen bonds, which endow the composite hydrogel with good self-healing property (SHP) and mechanical properties (MPs). The effect of BC content (BCC) on MPs and ionic conductivity (IC) of CHEPVA/BC were discussed. The results show that the composite hydrogel with BCC of 0.6% has the best SHPs and MPs, with breaking strength and IC as high as 0.41 MPa and 138.9 mS/cm, respectively. After the first healing cycle (FHC), IC and healing rate still reach 84.1 mS/cm and 74%, respectively. Polyaniline electrode was polymerized in-situ on the surface of the self-healing CHEPVA/BC, and a flexible all-in-one supercapacitor was designed and assembled. The results show that when aniline concentration is 0.2 mol/L, the supercapacitor device achieves high specific capacitance (580.8 mF/cm2), excellent energy density (20.17 μW·h/cm2) and power density (50 μW/cm2) at current density of 0.2 mA/cm2, and the capacitance retention rate after the FHC reaches 66%, showing good self-healing performance and great potential to maintain mechanical integrity and electrochemical stability. These findings indicate that the self-healing CHEPVA/BC has great application prospects in flexible wearable energy storage devices.
Abstract: Acetol and lactic acid are valuable platform chemicals that have a broad range of industrial applications and their production from renewable cellulose is of scientific and practical significance. A series of Sn-Fe@C catalysts were prepared by sol-gel and high-temperature annealing method in an inert atmosphere and then used for preparing acetol and lactic acid by one-step hydrogenolysis of cellulose in aqueous system. 3Sn1Fe@C600 as catalyst, the total acetol and lactic acid yield of 45.4% were obtained at 240 ℃ for 1 h under H2 atmosphere, of which the yields of acetol and lactic acid were 24.3% and 21.1%, respectively. The results indicated that the yield of acetol and lactic acid was strongly dependent on the Sn/Fe ratio of the catalyst as well as the annealing temperature. The characterizations including BET, XRD, XPS, Py-FTIR and CO2-TPD were carried out to explore the relationship between the structure of catalysts and catalytic activity. The strong L acid sites, basic sites and the metal active sites of the catalyst were the key factors affecting the selective production of acetol and lactic acid from cellulose hydrogenolysis.
Abstract: Adsorption of CO on ideal and oxygen deficient Cu1/CeO2(110) surfaces was studied by density functional theory (DFT), and the adsorption characteristics of CO molecules at different sites on the modelled catalyst surface were calculated and analyzed. The results show that Cu-doping can significantly improve the adsorption performance of CO on the catalyst surface. The top position is the most stable adsorption site of CO, but the adsorption of CO on empty acupoints is very weak. Compared with the ideal surface, the linear defect structure can promote the adsorption of CO on the catalyst surface. The PDOS analysis of adsorption configuration shows that a large number of orbital hybridization may be the reason for the strong adsorption performance of CO on Cu1/CeO2(110) surface.
Abstract: Ce0.8Zr0.2O2 solid solutions were synthesized by hydrothermal method, and active components were loaded by impregnation method to get CuO/Ce0.8Zr0.2O2 catalysts. Effects of citric acid content on the structure, properties and hydrogen production performance of CuO/Ce0.8Zr0.2O2 catalysts were investigated. CuO/Ce0.8Zr0.2O2 catalysts prepared with different citric acid content are distinct in Cu surface area, reduction performance and interaction between Ce0.8Zr0.2O2 solid solution and CuO. Among them, the catalyst prepared with a citric acid concentration of 0.04 mol/L has a large Cu surface area, a low CuO reduction temperature and a strong interaction between Ce0.8Zr0.2O2 solid solution and CuO, which has the best catalytic activity and the highest CO conversion in the water gas shift conversion process. At 320 ℃, water/gas molar ratio n(H2O)/n(CO) = 2, total volume velocity GHSV = 6600 h−1, its CO conversion is 96.9% close to thermodynamic equilibrium value.
Abstract: The early stage co-pyrolysis of typical plastic waste including polyethylene (PE), polypropylene (PP) and polystyrene (PS) were investigated by using the reactive force field molecular dynamics (ReaxFF MD) simulation with an automatic reaction mechanism analysis software (AutoRMA); the kinetic model, product yields and reaction process of co-pyrolysis were analyzed at atomic level. The results show that the kinetic parameters of PE/PP/PS co-pyrolysis can be obtained through the weighted sum of the parameters for the fracture of C–C and C–H bonds; the estimated activation energy is very close to the experimental one with a small error of ±3.86%, indicating that the fracture of C–C and C–H bonds can accurately characterize the co-pyrolysis process. For the co-pyrolysis of PE-PP mixture, an increase of PP content can improve the yields of oil and combustible gas, whereas for the co-pyrolysis of PP-PS mixture, the increase of PS content can improve the yields of tar and oil. In contrast, for the co-pyrolysis of PE-PP-PS mixture, a higher temperature is beneficial for the conversion of heavy oil into light oil; the light oil content increases from 44.77% at 2400 K to 56.18% at 3000 K. In addition, as a higher temperature can promote the further cracking of light hydrocarbons into gas products of smaller molecules, the yields of H2 and CH4 increase significantly with the increase of pyrolysis temperature, whereas the yields of C2H4 and C3H6 increase first and then decrease with the temperature. In comparison with the separated pyrolysis, the co-pyrolysis commences later, but displays shorter time to reach the first equilibrium state and generates products with smaller molecules. For the separate pyrolysis of PE and PP, their monomers emerge first, hereafter the alkanes and small molecule gases are produced; for the co-pyrolysis process, in contrast, the alkanes and small molecule gases are generated prior to the monomers. Moreover, PS tends to provide ·H radicals in the co-pyrolysis process, which can combine with the free radicals generated from PE and PP pyrolysis, forming small molecule alkanes and H2.
Abstract: A series of manganese-doped VWTi catalysts were prepared by the sol-gel method, and the denitrification performance of the catalysts in a wide temperature range was tested on a fixed bed reactor to examine the influences of catalyst preparation process, flue gas components, reaction temperature, gas hourly space velocity on denitrification activity of the catalyst. The catalyst was characterized and analyzed by means of BET, XRD, XPS, SEM and H2-TPR. The results show that Mn doping significantly improves the denitrification efficiency of the catalyst in the range of 200–300 ℃, and a lower drying temperature is beneficial to improve the denitrification activity of the catalyst. The characterization results of the catalyst show that with the drying temperature increase, the TiO2 on the catalyst surface changes from anatase crystal form to rutile crystal form, the proportion of chemically adsorbed oxygen on the surface of the catalyst is significantly reduced, the proportion of high valence manganese is reduced, the proportion of manganese and vanadium as the active components of the catalyst surface is significantly reduced, and the low-temperature reduction peak of the catalyst gradually disappears. These all reduce the catalytic oxidation activity of catalysts.
Abstract: Catalytic oxidation of NO (CONO) at ambient temperature over sludge char (SC) prepared from sewage sludge was studied in this paper. The influencing mechanism of sludge pyrolysis/activation parameters on the CONO were investigated for the SC prepared with different pyrolysis temperatures (600, 700, and 800 ℃) and different mass ratios of dried sludge (DS) to KOH (DS/KOH = 4∶1, 3∶1, 2∶1, and 1∶1). The results indicated that both pyrolysis temperature and KOH activation had great influence on the catalytic performance of SC. With the increase of temperature from 600 to 800 ℃, the NO conversion increased from 12% to 36%. However, the catalytic activity of KOH-activated SC increased and then decreased with the increase of KOH content. The SC prepared under the pyrolysis temperature of 700 ℃ and the DS/KOH mass ratio of 3∶1 showed the best catalytic performance with NO conversion of 56%. The NO conversion further increased to 76.5% when the SC was reduced by H2. It was also found that there was a strong correlation between the catalytic activity and the specific surface area of the SCs. The reaction might follow the Eley-Rideal (E-R) mechanism.
Abstract: In this study, the feasibility of using ethylene tar (ET) as raw material for needle coke production was investigated. The basic properties, structural compositions, and thermal stability of ethylene tar and its narrow fractions were studied by elemental analysis, Fourier transform-infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), the coke induction period, and simulation of thermal stability of coking feed. The properties of the products were analyzed by a polarized light microscope, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the content of asphaltenes was up to 22.04% in ET, and the thermal stability was poor due to the high content of olefin and other thermally sensitive components. Thus, the coke induction period of ET was only 34 min. After distillation, narrow fractions had no asphaltenes and a low quantity of heat-sensitive components, resulting in improved fraction thermal stability with coke induction period of more than 55 min. Due to its narrow molecular distribution and low content of heat-sensitive components of narrow fractions, the semi-cokes formed from narrow fractions possessed better anisotropic and microcrystalline structures than those formed from the ET. Compared with one-stage carbonization, the two-stage carbonization was more conducive to the coalescence, development, and orientation of mesophase, leading to the formation of a fibrous wide-area streamline structure. The needle coke prepared from the fraction of ET-C had a lower thermal expansion coefficient (CTE), as low as 2.49 ×10−6 ℃−1, meeting the CTE requirement of needle coke.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
