Evaluation, Reduction, and Validation of a New Skeletal Mechanism for the Cofiring of NH3 and CH4.

The evaluation and reduction of kinetic models for the cofiring of NH3 and CH4 can help to guide the application of NH3 and CH4 in industrial equipment. In this work, eight detailed kinetic models on the cofiring of NH3 and CH4 and 15 detailed kinetic models on the NH3 combustion are collected and evaluated based on error function and experiment measurement, and the detailed mechanism of 169 species and 1268 elementary reactions with the best overall performance was determined. By using two mechanism reduction methods of directed relation graph with error propagation (DRGEP) and DRGEP with sensitivity analysis (DRGEPSA), the skeletal mechanism of 45 species and 344 elementary reactions is achieved within the temperatures of 1000-2000 K, pressures of 1-60 atm, and equivalence ratios of 0.5-2.0. The skeletal mechanism is comprehensively validated and achieves good consistency with the detailed mechanism in predicting the laminar burning velocity, species concentration, and ignition delay time. The maximum relative error between the skeletal mechanism and the detailed mechanism is less than 13%.

Thermal oxidation of degradation products from thermoplastic polyvinyl alcohol: Determination on oxidation temperature and residence time.

The degradable protective articles made of thermoplastic polyvinyl alcohol (TPVA) are widely used in nuclear power plants, and they are thermally decomposed after use to reduce solid waste. However, in the real decomposition of TPVA, the temperature in the oxidation reactor is not self-sustaining; as a result, the degradation products contain a lot of CO, resulting in more pollution and energy waste. In this paper, jet stirred reactor (JSR) and Chemkin software were used to study the reaction kinetics characteristics of the oxidation process of degradation products from TPVA in the range of 550 °C-700 °C. Both experiments and kinetic simulation show that a higher average temperature of the oxidation reactor is needed to achieve lower CO emissions. When using 5% or 10% TPVA degradation solution, the average temperature should not befall below 625 °C or 675 °C. The corresponding residence time should be greater than 6 s and 5 s respectively. The combination of research findings and engineering practice provides great help to the optimization of the actual work process.

Emission characteristics of coal gasification fine slag direct combustion and co-firing with coal.

Coal gasification is an effective way to use coal cleanly and efficiently, and coal gasification fine slag is a by-product of coal gasification with high carbon content, large specific surface area, developed pore structure and large output during production. At present, combustion has become an effective way to dispose of coal gasification fine slag on a large scale, and the coal gasification fine slag after combustion treatment can be further used for construction raw materials. In this paper, the emission characteristics of gas-phase pollutants and particulate matter under different combustion temperatures (900 °C, 1100 °C, 1300 °C) and combustion atmosphere (5%, 10%, 21% O2 concentration) are studied with the drop tube furnace experimental system. By co-firing different proportions of coal gasification fine slag (10%, 20%, 30%) and raw coal, the pollutants formation law under co-firing conditions is studied. Scanning electron microscopy-energy spectroscopy (SEM-EDS) is used to characterize the apparent morphology and elemental composition of particulate samples. The measurement results of gas-phase pollutants show that the increase of furnace temperature and O2 concentration can effectively promote combustion and improve burnout characteristics, but the emission of gas-phase pollutants increases. A certain proportion (10%-30%) of coal gasification fine slag is added to the raw coal, which reduces the total emission of gas-phase pollutants (NOx and SOx). Studies on the characteristics of particulate matter formation show that co-firing with coal gasification fine slag in raw coal can effectively reduce submicron particle emission, and the lower fine particle emission is also detected at lower furnace temperature and oxygen concentration. The element analysis of particulate matter formation shows that the Fe, Si and S elements content of submicron particle generated by YL (the coal gasification fine slag generated by water slurry furnace in of Shaanxi Extended China Coal Yulin Energy Chemical Co., Ltd) sample increases significantly with the increase of furnace temperature and O2 concentration, which is the main influencing factor for the increase of submicron particle. With the increase of the mixing ratio of YL sample, the content of major elements such as Fe, K and Mg of submicron particle decreases significantly, which is an important reason why the amount of the submicron particle decreases.

Process design and optimization on self-sustaining pyrolysis and carbonization of municipal sewage sludge.

Pyrolysis can realize the reduction and resource utilization of municipal sewage sludge (MSS). In this paper, a self-sustaining pyrolysis process is designed for municipal sewage sludge, and the process flow is simulated by Aspen plus software. By changing the initial moisture content of sludge, moisture content after drying, pyrolysis temperature and air supply in the incinerator, the possibility of achieving energy self-balance in the system is analysed. The simulation results show that by adjusting the parameters of the system, this process can realize the energy self-balance of sludge drying and pyrolysis treatment. Considering the system's energy loss, the dry basis calorific value of sludge should not be less than 10 MJ/kg. The higher the initial moisture content of sludge, the more external energy input the system needs. It is recommended to dehydrate sludge mechanically to about 60 % before entering the system. When the pyrolysis temperature is increased, the amount of oil and gas produced by sludge pyrolysis increases, and it is easier to achieve self-balance of system energy. But the higher the pyrolysis temperature, the greater the energy consumption required. In practice, it is suggested that the pyrolysis temperature is about 400 °C. The moisture content of dried sludge has little effect on the energy self-balance of the system, and it is recommended to be about 30 %. The air supply volume of the incinerator mainly affects the flue gas outlet temperature and flue gas volume, but has little effect on the energy balance of the system.

Optimization of Dechlorination Experiment Design Using Lightweight Deep Learning Model.

This exploration intends to remove chloride ions in production and life, enhance buildings' durability, and protect the natural environment from pollution. The current dechlorination technology is discussed based on the relevant theories, such as the lightweight deep learning (DL) model and chloride ion characteristics. Next, data statistics and comparative analysis methods are used to study the adsorption and desorption performance of dechlorination adsorbents. Finally, the lightweight DL model is introduced into the chloride diffusion prediction experiment of slag powder and fly ash concrete. The results show that in the study of dechlorination adsorption performance, the chloride ion concentration decreases gradually with the extension of adsorption time. However, with the increasing temperature, the chloride ion removal rate is increasing. The removal rate of chloride ions in water can decrease slowly with the increase of adsorbent. Therefore, selecting the 2 mol/L sodium hydroxide as the alkali concentration for adsorbent regeneration is the most appropriate. Besides, the regeneration performance of the adsorbent gradually declines with the increase of sodium chloride concentration in the solution. The lightweight DL model is applied to the chloride diffusion prediction experiment of slag powder and fly ash concrete. It is found that when the curing age is selected at 18 days, 90 days, and 180 days, respectively, the error between the lightweight DL model and the experimental results is about 0.2. It shows that the lightweight DL model is feasible for predicting the diffusion of chloride ions. Therefore, this exploration designs and studies the dechlorination experiment based on the lightweight DL model, which provides a new theoretical basis and optimization direction for removing chloride ions in the future industry.

Distribution characteristics of soil AM fungi community in soft sandstone area.

To explore the diversity and distribution characteristics of soil arbuscular mycorrhizae fungi (AMF) communities in the soft sandstone area, thirteen arsenic sandstone rock samples were collected from three planting plots (SI, SII and SIII) and one bare control plot (CK), separately. The sampling locations are as follows: the top of the slope (denoted by the number 1), sunny slope (2), shady slope (3) and gully bottom (4). These samples were then tested with an Illumina HiSeq PE250 high-throughput sequencing platform. Experimental results show that the SIII4 sample (from the gully bottom of the SIII plot) has the highest moisture content of 9.1%, while the CK sample in the control plot has lowest moisture content. SI2 has the highest pH of 9.58 and CK has the lowest pH of 8.73. SII1 has the highest available phosphorus (AP) content of 9.61 mg/kg, while SII3 has the lowest AP content of 2.29 mg/kg. Furthermore, SI2 has the highest NH4-N content of 11.24 mg/kg, while SII1 has the lowest NH4-N of 4.09 mg/kg. SII1 has the highest available potassium (AK) content of 48.92 mg/kg and CK has the lowest AK content of 1.82 mg/kg. In the observed-species index reflecting AMF genetic diversity, SI1 differences significantly from SII4 and SIII3 (P < 0.05). In the Shannon index, SI1 is significantly different from SI2, SI3, SI4; SII2 is significantly different from SII3; SI2, SI4, SII1 and SII3 are quite different from CK (P < 0.05). The dominant genera of AMF in these plots include Glomus (17.24%-65.53%), Scutellospora (0.04%-67.38%), Septoglomus (2.83%-43.03%) and Kamienskia (0.64%-46.38%). The dominant genera of AMF vary significantly between sunny slope and shady slope. Positive correlation exists between soil NH4-N and the AM fungal community structure. There are prominent positive correlations exist among genetic diversity index chao1, observed-species, pH and AP (P < 0.05), and obviously negative correlation between observed species and AK (P < 0.05). The research findings on the distribution characteristics of AM fungus community in the arsenic sandstone plot and their relationship with environmental factors can help with arsenic sandstone management in other similar areas.

Submicron particle formation from co-firing of coal and municipal sewage sludge.

With the increasing production of municipal sewage sludge (MSS) in China every year, the co-firing of MSS and pulverized coal is getting more and more widely applied in large coal-fired power plants. The co-firing of MSS and pulverized coal will produce a large amount of particulate matter (PM) emissions, especially submicron particles. In this paper, the formation characteristics of submicron particles in the co-firing process of coal and MSS were studied in a drop tube furnace. The influence of the furnace temperature and the addition ratio of sludge on the particle size distribution and element composition of submicron particles in MSS, pulverized coal combustion and co-firing was mainly studied. The experimental results show that the furnace temperature has an influence on the formation of PM0.4. For sludge combustion, increasing the furnace temperature will promote the formation of PM0.4. The main reason is that increasing the furnace temperature promotes the gasification of Si, S, Fe, and P to form the precursor of PM0.4 or PM0.4. At same furnace temperature, the volume concentration and mass concentration of PM0.4 produced from pulverized coal combustion are less than that of sludge. Different from sludge combustion, co-firing of pulverized coal and sludge has a synergistic effect on eliminating PM0.4 formation. Increasing the addition ratio of sludge can decrease the volume concentration and mass concentration of PM0.4. This is because that aluminosilicates formed during co-firing promotes the scavenge Si, Ca, Fe, thereby reducing the precursors of PM0.4 and the mass yield of PM0.4. Increasing the furnace temperature in co-firing can inhibit the formation of PM0.4. When the furnace temperature is between 1100 °C and 1300 °C, increasing the furnace temperature will reduce the Fe content and increase the content of Si, Ca, Na, K, and P in PM0.4. However, the reduction of Fe and the increase of Si, Ca, Na, K, and P in PM0.4 offset each other, resulting in an insensitive relationship between the mass yield of PM0.4 and the furnace temperature.

Numerical Simulation on the Effect of Burner Bias Angles on the Performance of a Two-Stage Entrained-Flow Gasifier.

A 2000 t/day HNCERI (Huaneng Clean Energy Research Institute) entrained-flow pulverized coal gasifier suffers from the problem of a high ash-slag ratio. An appropriate bias angle of the burners is the key to solve this issue for the gasifier with a specific structure. A random pore model considering bulk and pore diffusion effects was extended by user-defined function to describe the gasification reactions. The simulation of the gas flow and char gasification characteristics under different bias angles (0, 1.5, 2.5, 3.5, and 4.5°) of the four burners in the first stage was conducted. The simulation results showed favorable agreement with the industrial data. The evaporation, devolatilization, and char oxidation mainly occurred in the first-stage jet zone, and the upflow and downflow zones are dominated by the gasification reactions. The bias angles of the burners mainly affect the scale of gasification reaction zones. As the bias angles increased from 0 to 4.5°, the gas temperature at the slag tap hole decreased from 1880 to 1500 K. The carbon conversion efficiency of the first stage decreases and that of the second stage increases with the bias angle increasing. An optimal bias angle of 2.5° is recommended for the HNCERI gasifier with a total carbon conversion efficiency of 98.16%.

A kinetic evaluation and optimization study on NOx reduction by reburning under pressurized oxy-combustion.

Pressurized oxy-combustion is an emerging and more efficient technology for carbon capture, utilization, and storage than the first generation (atmospheric) oxy-combustion. NOx is a major conventional pollutant produced in pressurized oxy-combustion. In pressurized oxy-combustion, the utilization of latent heat from moisture and removal of acid gases (NOx and SOx) are mainly conducted in an integrated direct-contact wash column. Recent studies have shown that NOx particular inlet concentration should be maintained before direct contact wash column to remove NOx and SOx efficiently. As a result, minimizing NOx for environmental reasons, avoiding corrosion in carbon capture, utilization, and storage, and achieving effective NOx and SOx removal in direct contact wash columns are crucial. Reburning is a capable and affordable technology for NOx reduction; however, this process is still less studied at elevated pressure, particularly in pressurized oxy-combustion. In this paper, the kinetic evaluation and optimization study on NOx reduction by reburning under pressurized oxy-combustion was conducted. First, the most suitable mechanism was selected by comparing the results of different kinetic models with the experimental data in literature at atmospheric and elevated pressures. Based on the validated mechanism, a variety of parameters were studied at high pressure, i.e., comparing the effects of oxy and the air environment, different reburning fuels, residence time, H2O concentration, CH4/NO ratio, and equivalence ratio on the NO reduction. The results show that de-NOx efficiency in an oxy environment is significantly enhanced compared to the air environment. Improvement in the de-NOx efficiency is considerably higher with a pressure increase of up to 10 atm, but the effect is less prominent above 10 atm. The formation of HCN is significantly reduced while the N2 formation is enhanced as the pressure increases from 1 to 10 atm. The residence time required for the maximum NO reduction decreases as the pressure increases from 1 atm to 15 atm. At the higher pressure, the NO reduction rises prominently when the ratio of CH4/NO increases from 1 to 2; however, the effect fades after that. At higher pressure, the NO reduction by CH4 reburning decreases as the H2O concentration increases from 0 to 35%. The optimum equivalence ratio and high pressure for maximum NO reduction are 1.5 and 10 atm, respectively. This study could provide guidance for designing and optimizing a pressurized reburning process for NOx reduction in POC systems.

Combustibility analysis of high-carbon fine slags from an entrained flow gasifier.

The fine slag produced from the entrained flow gasifier in coal chemical industry contains a high amount of unburned carbon content, which can reach more than 40%. The coal gasification fine slag is dissipated just by land filling which occupies a lot of land. Consequently, it causes the pollution of soil, water and wastes the combustible carbon in coal gasification fine slag. It is crucial to develop an environmental friendly and economical scheme for the utilization of coal gasification fine slag. To achieve this aim, it is significant to investigate the combustibility of coal gasification fine slag and then propose a comprehensive utilization technology. In this study, the physical and chemical properties of the raw bituminous coal and the produced coal gasification fine slag, including proximate and ultimate analysis, particle size distribution, ash composition, morphology, and specific area were investigated. The combustion and co-combustion characteristics of coal gasification fine slag were analyzed by a thermo-gravimetric analyzer. A drop tube furnace and a fluidized bed reactor were employed to test the combustibility of coal gasification fine slag in a pulverized furnace and a fluidized bed furnace, respectively. Results show that the carbon content in dried coal gasification fine slag is >40% with a heating value > 16 MJ kg-1. Further, thermo-gravimetric analyzer test showed that the combustion property of coal gasification fine slag is worse than that of anthracite and close to that of high ash coal, and there is a non-negligible synergistic effect for raw bituminous coal and coal gasification fine slag co-firing. The combustibility test in drop tube furnace and fluidized bed reactor showed that coal gasification fine slag can be well burned in a pulverized furnace requiring combustion temperature >900 °C and oxygen concentration >10 vol%. However, the fluidized bed furnace was not appropriate for high efficiency coal gasification fine slag burning, because the unburned carbon content of fly ash after coal gasification fine slag combustion is still >14%, even at 900 °C, 21% oxygen concentration and a low fluidization number. It is suggested that coal gasification fine slag will be better to burned it in a pulverized furnace rather than fluidized furnace.

Effect of thermal expansion additives on alleviating the ash deposition of high-sodium coal.

The high content of sodium in coal ash can induce severe ash deposit problems on heated surface. Vermiculite has been investigated to solve this problem in drop-tube furnace recently. In this work, the effects of vermiculite and perlite on appearances, inorganic mineral transformation, elemental composition change and Na capture efficiency of ash deposit were investigated. The results show that the molten deposit obtained by drop-tube furnace at 1373 K was transformed into weakly-condensed deposit and strongly-sticky deposit respectively when vermiculite and perlite were added separately. Vermiculite has a better effect on improving the ash deposition than perlite. The mechanism of alleviating the ash deposition by vermiculite and perlite is proposed as follows: (1) The interaction between ash particles is inhibited due to the combination reactions of thermal expansion additive particles with coal ash particles. (2) The coal ash particles attach to the surface and the gap of thermal expansion additive particles, forming a porous structure. (3) With vermiculite added, Mg2SiO4 (forsterite) increases the fusion point of ash deposit. NaCa2Mg4Al(Si6Al2)O22(OH)2 (pargasite) and Mg1.8Fe0.2SiO4 (forsterite ferroan) result in the weak viscosity of ash deposit. (4) With perlite added, silicate and sodium aluminosilicate in perlite react with coal ash to produce a large amount of amorphous substance, which can flow downwards to make the bottom deposit molten and lead to the strong viscosity of total deposit. (5) Vermiculite has a strong capacity for Na capture at 1023 K, and perlite has a strong capacity for Na capture at 1373 K.

Catalytic function of ferric oxide and effect of water on the formation of sulfur trioxide.

Sulfur trioxide (SO3) is not only environmentally harmful but also highly corrosive, taking a great threat to the safe operation of coal-fired power plants. A dominant pathway of SO3 formation in coal-fired power plant is through the catalytic oxidation of SO2 (SO2+1/2O2→SO3) on the surfaces of ash particles containing Fe2O3. The catalytic formation of SO3 could be affected by complex atmosphere, where the effect from H2O is still debatable. In this paper, density functional theory (DFT) is employed to explore the reaction pathway of SO3 formation catalyzed by α-Fe2O3 in complex atmosphere containing O, O2, SO2 and H2O. In order to get the stable adsorption sites of these species, the adsorption energy of potential adsorption configurations on the α-Fe2O3 (001) surface is calculated. The dissociations of O2 molecule on complete and defect α-Fe2O3 (001) surfaces with O vacancy are calculated, and the Langmuir-Hinshelwood and Eley-Rideal mechanisms for the O(ads) reaction with SO2(ads) or SO2 are compared. The effect of H2O besides of SO2 and O2 on the formation of SO3 is especially discussed. The DFT calculation results show that for the formation of SO3 in gas phase, the energy barrier of 'SO2+1/2O2→SO3' is 436.75 kJ mol-1, in contrast, for the catalytic formation of SO3 on α-Fe2O3 surfaces, this energy barrier becomes an order of magnitude smaller, 24.82 kJ mol-1. O2 molecules can dissociate on the defect α-Fe2O3 (001) surface with O vacancy spontaneously, indicating that the defect α-Fe2O3 is favorable for the dissociation of O2, thereby promotes the formation of SO3. The energy barrier of 'SO2(ads)+O(ads)→SO3(ads)' through Langmuir-Hinshelwood mechanism is much higher than that of 'SO2+O(ads)→SO3(ads)' through Eley-Rideal mechanism. The adsorption energy on the α-Fe2O3 (001) surface of H2O is much smaller than that of SO2 and O2, indicating that H2O has little effect on the adsorption of O, O2, SO2 and eventually the heterogeneous formation of SO3. The DFT analysis results in this study provide a deep understanding on the reaction pathway of SO3 catalytic formation by Fe2O3.

Hot corrosion behaviors of TP347H and HR3C stainless steel with KCl deposit in oxy-biomass combustion.

Oxy-combustion is one of the most promising technologies for carbon capture and sequestration. When CO2-neutral biomass is burned under oxy-combustion conditions, named "oxy-biomass combustion" a negative CO2 emission can be achieved. However, the high content of potassium and chlorine in biomass results in sever ash deposition and corrosion in air fired furnaces, which are further aggravated in oxy-combustion mode due to the enrichment of corrosive species by flue gas recycle. In this paper, the hot corrosion behaviors and mechanism of two representative materials (TP347H, HR3C) used for superheaters in furnaces are studied. The effects of oxy-combustion atmosphere, KCl deposition, effect of SO2, effect of water vapor, and temperature on the corrosion kinetics at the starting stage are investigated. The corrosion severity of the materials was determined using the weight gain method, and the microstructures and chemical compositions of corrosion layers were characterized by the scanning electron microscopy with energy dispersive spectroscopy, and X-ray diffraction. The results show that the hot corrosion rate is significantly sped up by KCl deposition, more than five times the gas corrosion rate under the same gas composition and temperature. HR3C with higher Cr and Ni contents is more likely to form Cr enrichment on the interface between the corrosion layer and the substrate than TP347H, resulting in stronger resistance to the hot corrosion than TP347H. When the corrosion atmosphere is changed from air-combustion to oxy-combustion, the hot corrosion rate is reduced with a denser Cr oxide film and less metal sulfides. The increase of temperature in the presence of KCl deposition significantly affects the hot corrosion rate, e.g. the corrosion rate at 650 °C is 16 times higher than that at 450 °C. Water vapor and SO2 concentrations have opposite influences on the hot corrosion, respectively. Compared to the dry environment, a high-humidity environment decreases the hot corrosion rate; however, a higher SO2 concentration facilitates the sulfation of KCl deposits, leading to stronger damage to the chromium oxide film and thereby an increased hot corrosion rate.

Synergistic effect of biomass and polyurethane waste co-pyrolysis on soot formation at high temperatures.

Soot is an important toxic pollutant generated during high-temperature incineration of solid waste (i.e., biomass and plastic waste) under air-lean conditions, and has a great impact on flame radiation. The main objective of this work is to study the synergistic effect of biomass and polyurethane co-pyrolysis on soot formation at high temperatures (1100-1250 °C). The effects of temperature, biomass species, and co-pyrolysis ratio on the yield, morphology, composition and reactivity of soot particles are studied. Results show that under controlled co-pyrolysis conditions, the measured soot yield from co-pyrolysis of biomass and polyurethane is lower than the theoretical value by weight average, while the particle size distribution tends to concentrate on a smaller diameter range. The degree of synergistic effect increases with the increasing biomass ratio (0-50 wt%) and decreasing pyrolysis temperature. Wood in co-pyrolysis presents a stronger synergistic effect on soot yields than straw co-pyrolysis does. Degree of synergistic effect on soot oxidation reactivity depends much on the biomass addition ratio but less on pyrolysis temperature. At 10 wt% straw addition ratio, co-pyrolysis exerts a negative synergistic effect on soot oxidation reactivity, while the synergistic effect turns significantly positive when the straw addition ratio increases to 50 wt%.

Experimental and kinetics study on SO3 catalytic formation by Fe2O3 in oxy-combustion.

Sulfur trioxide (SO3) is corrosive and environmentally harmful. Under oxy-combustion mode, the formation of SO3 is aggravated due to flue gas recirculation, and should be more concerned than that under traditional air-combustion mode. In this paper, the catalytic formation of SO3 by iron oxide (Fe2O3) under oxy-combustion mode was experimentally studied in a fixed-bed reactor, and effects of temperature (300-900 °C), atmosphere, catalyst particle size, SO2, O2, and H2O concentrations were discussed. Results show that Fe2O3 promotes SO3 formation, and the yield of SO3 reaches a maximum at 700 °C under both air- and oxy-combustion modes. Increasing O2 concentration in a range of 5-20% promotes the catalytic formation of SO3, whose effect is restricted at a higher O2 concentration. Both increases of SO2 concentration in a range of 500-3000 ppm and steam concentration in a range of 0-20% decrease the SO3 yield. A significant effect of Fe2O3 particle size on SO3 catalytic formation is observed. When the particle size decreases from 50-75 µm to 10-25 µm, the inflection temperature shifts from 700 °C to 600 °C, while the maximum SO3 yield increases by 33%. Kinetics analysis results show that in this case, the catalytic conversion from SO2 to SO3 by Fe2O3 has an apparent activation energy Ea of 18.9 kJ/mol and a pre-exponential factor A of 5.2 × 10-5. At 700 °C and with Fe2O3 particle size of 50-75 µm, the global reaction orders of SO2 and O2 for SO3 formation are 0.71 and 0.13, respectively.

[Particle Removal Characteristics of an Ultra-low Emission Coal-fired Power Plant].

A 660 MW unit of an ultra-low emission coal-fired power plant in the Beijing-Tianjin-Hebei area was chosen for this study. The particulate matter was sampled with a Dekati low-pressure impactor (DPLI) at the inlet and outlet of flue gas cleaning devices including selective catalytic reduction (SCR), low-low temperature economizer (LLTe), electrostatic precipitator (ESP), wet flue gas desulfurization (WFGD), and wet electrostatic precipitator (WESP). A filter sampling system was also used at the inlet and outlet of the WFGD and WESP. The removal efficiencies of PM1, PM1-2.5, and PM2.5-10 from different flue gas cleaning devices were obtained after ultra-low emission modification. The results show that SCR increases the mass concentration of fine particulates and PM1 by 52.11%. The LLTe improves the removal efficiency of the ESP, especially for particles with a range of 0.1-1 µm. The high-efficiency WFGD removes both SO2 and particulates, but it increases PM1. The mass concentration of PM1 increases by 59.41% and the water-soluble Mg2+, Cl-, and SO42- in PM10 increases. The WESP has a high removal efficiency with respect to PM1, PM1-2.5, and PM2.5-10 and can further reduce the dust concentration. Based on an ultra-low emission reform, the final PM10 emission of this 660 MW unit is 2.04 mg·m-3.

PM2.5 exposure during pregnancy induces hypermethylation of estrogen receptor promoter region in rat uterus and declines offspring birth weights.

Particulate matter 2.5 (PM2.5) exposures during pregnancy could lead to declined birth weight, intrauterine developmental restriction, and premature delivery, however, the underlying mechanisms are still not elucidated. There are few studies concerning the effects of PM2.5 exposure on maternal and child health in Xi'an (one of the cities with severe air pollution of PM2.5 in North China). Then, this study aimed to investigate the effect of PM2.5 exposure in Xi'an on the offspring birth weights and the possibly associated epigenetic mechanisms. We found the Low and High groups: the offspring with declined birth weights; the decreased mRNA and protein expression of the estrogen receptor (ERs) and eNOs in the uterus; the decreased endometria vascular diameter maximum (EVDM); the increased mRNA and protein expressions of the DNMT1 and 3b in the uterus; the elevated methylation levels of the CpG sites in the CpG island of ERα promoter region in the uterus. However, no differences were observed in the mRNA or protein expressions of ERß and DNMT3a between the Clean and PM2.5 exposure groups, as well as endometriavascular density (EVD). Additionally, PM2.5 level was negatively correlated with the ERα protein expression, EVDM and offspring birth weight, as well as the methylation level of the CpG sites in the CpG island of ERα promoter region and the ERα protein expression in the uterus; whereas the ERα protein expression was positively correlated with the offspring birth weight, as well as PM2.5 level and the methylation level of the CpG sites in the CpG island of ERα promoter region in the uterus. Taken together, elevated methylation level of the CpG sites in the CpG island of ERα promoter region reduces ERα expression in the uterus, which could be one of the epigenetic mechanisms that pregnant PM2.5 exposure reduces the offspring birth weights.

Low NOx combustion and SCR flow field optimization in a low volatile coal fired boiler.

Low NOx burner redesign and deep air staging have been carried out to optimize the poor ignition and reduce the NOx emissions in a low volatile coal fired 330 MWe boiler. Residual swirling flow in the tangentially-fired furnace caused flue gas velocity deviations at furnace exit, leading to flow field unevenness in the SCR (selective catalytic reduction) system and poor denitrification efficiency. Numerical simulations on the velocity field in the SCR system were carried out to determine the optimal flow deflector arrangement to improve flow field uniformity of SCR system. Full-scale experiment was performed to investigate the effect of low NOx combustion and SCR flow field optimization. Compared with the results before the optimization, the NOx emissions at furnace exit decreased from 550 to 650 mg/Nm³ to 330-430 mg/Nm³. The sample standard deviation of the NOx emissions at the outlet section of SCR decreased from 34.8 mg/Nm³ to 7.8 mg/Nm³. The consumption of liquid ammonia reduced from 150 to 200 kg/h to 100-150 kg/h after optimization.

A kinetic study on the catalysis of KCl, K2SO4, and K2CO3 during oxy-biomass combustion.

Biomass combustion under the oxy-fuel conditions (Oxy-biomass combustion) is one of the approaches achieving negative CO2 emissions. KCl, K2CO3 and K2SO4, as the major potassium species in biomass ash, can catalytically affect biomass combustion. In this paper, the catalysis of the representative potassium salts on oxy-biomass combustion was studied using a thermogravimetric analyzer (TGA). Effects of potassium salt types (KCl, K2CO3 and K2SO4), loading concentrations (0, 1, 3, 5, 8 wt%), replacing N2 by CO2, and O2 concentrations (5, 20, 30 vol%) on the catalysis degree were discussed. The comparison between TG-DTG curves of biomass combustion before and after water washing in both the 20%O2/80%N2 and 20%O2/80%CO2 atmospheres indicates that the water-soluble minerals in biomass play a role in promoting the devolatilization and accelerating the char-oxidation; and the replacement of N2 by CO2 inhibits the devolatilization and char-oxidation processes during oxy-biomass combustion. In the devolatilization stage, the catalysis degree of potassium monotonously increases with the increase of potassium salt loaded concentration. The catalysis degree order of the studied potassium salts is K2CO3 > KCl > K2SO4. In the char-oxidation stage, with the increase of loading concentration the three kinds of potassium salts present inconsistent change tendencies of the catalysis degree. In the studied loading concentrations from 0 to 8 wt%, there is an optimal loading concentration for KCl and K2CO3, at 3 and 5 wt%, respectively; while for K2SO4, the catalysis degree on char-oxidation monotonically increases with the loading potassium concentration. For most studied conditions, regardless of the potassium salt types or the loading concentrations or the combustion stages, the catalysis degree in the O2/CO2 atmosphere is stronger than that in the O2/N2 atmosphere. The catalysis degree is also affected by the O2 concentrations, and the lowest catalysis degree is generally around 20 vol% O2 concentration. The kinetic parameters under the different studied conditions are finally obtained.

Investigation on the fast co-pyrolysis of sewage sludge with biomass and the combustion reactivity of residual char.

Gaining the valuable fuels from sewage sludge is a promising method. In this work, the fast pyrolysis characteristics of sewage sludge (SS), wheat straw (WS) and their mixtures in different proportions were carried out in a drop-tube reactor. The combustion reactivity of the residual char obtained was investigated in a thermogravimetric analyzer (TGA). Results indicate that SS and WS at different pyrolysis temperatures yielded different characteristic gas compositions and product distributions. The co-pyrolysis of SS with WS showed that there existed a synergistic effect in terms of higher gas and bio-oil yields and lower char yield, especially at the WS adding percentage of 80wt%. The addition of WS to SS increased the carbon content in the SS char and improved char porous structures, resulting in an improvement in the combustion reactivity of the SS char. The research results can be used to promote co-utilization of sewage sludge and biomass.