The effect of multiple factors on changes in organic-inorganic fractions of condensable particulate matter during coal combustion.

Condensable particulate matter (CPM) from coal combustion is the focus of current pollutant emission studies, and CPM can be divided into inorganic and organic fractions according to the component characteristics. At present, the effects of different factors in the combustion process on the organic and inorganic components of CPM have not been discussed systematically. Here, we conducted combustion experiments collected the generated CPM on a well-controlled drip tube furnace, and investigated the effects of different factors on the generation of organic and inorganic components of CPM by varying the furnace wall insulation temperature, the ratio of gas supply components and the water vapor content in the flue gas. The results showed that the increase in combustion temperature (1300-1500 °C) and oxygen concentration (15-25%) reduced the total CPM generation by 9.8% and 19.98%, respectively, and the intervention of water vapor increased the ability of the whole CPM sampling device to capture ultrafine condensable particles. The generation of CPM organic components decreased with the enhancement of combustion temperature and oxygen content on combustion characteristics, and alkanes shifted to low carbon content. The amount of CPM inorganic components increased with the increase of water vapor content in the flue gas, and this change was dominated by SO42-. The above results provide a feasible idea for the next step of the precise reduction of CPM components.

Co-hydrothermal carbonization of sludge and food waste for hydrochar valorization: Effect of mutual interaction on sulfur transformation.

Co-hydrothermal carbonization of sludge and food waste is a promising method for hydrochar valorization. The sulfur content and form of hydrochar are the key parameters that determine its further utilization. However, the effect of the chemical composition of food waste on sulfur redistribution remains unknown. Herein, the sulfur transformation behavior during the co-hydrothermal carbonization of sludge and model compounds (cellulose, starch, xylan, and palmitic acid) of food waste was investigated, with focus on the detailed reaction pathways from inorganic-S/organic-S media in aqueous to hydrochar. The added model compounds, particularly the starch and xylan, increased the sulfur retention ratio from 41.0 to 44.7- 49.2 % in hydrochar. Among them, starch and xylan can react with aliphatic-S in aqueous via cyclization and oxidization to form the thiophene-S/aromatic-S and sulfone-S and can react with SO42--S to form sulfone-S via sulfonate reaction. These formed organic-S can polymerize with hydrolyzed intermediates (i.e., 5 hydroxymethyl-furfural, glucose, and xylose) from model compounds to transform into hydrochar. Cellulose enhanced the formation of sulfone-S in hydrochar via the reactions between the water-insoluble partial hydrolysate and SO42- in the aqueous. Additionally, palmitic acid hydrolysate provided an acidic environment that facilitated the polymerization of thiophene-S/aromatic-S from aqueous to hydrochar. Generally, the chemical composition of food waste largely affects the redistribution behavior of sulfur during co-hydrothermal carbonization, and this occurs primarily due to the differences in the hydrolysate and degree of hydrolysis for various model compounds. The results can provide guidance for preparing sludge-based hydrochar possessing different sulfur content and species, that can be used as clean fuel or carbon material.

Application of zeolite synthesized from coal fly ash via wet milling as a sustainable resource on lead(II) removal.

In this work, zeolite based on coal fly ash was firstly synthesized via wet milling for the adsorption of lead (Pb(II)). The effects of contact time, solid-to-liquid ratio and initial pH of solution on Pb(II) removal were investigated in detail. The experimental data showed that synthesized zeolite has high adsorption capacity of 99.082 mg of Pb(II) per gram of adsorbent. Coal fly ash zeolite synthesized by wet milling has good Pb(II) adsorption performance when the initial pH of the solution is above 5. The adsorption kinetic results demonstrated that removal of Pb(II) via the synthesized zeolite followed pseudo-second-order kinetic model. X-ray photoelectron spectroscopy results directly demonstrated the adsorption between Pb(II) and synthesized zeolite, and a possible reaction pathway was proposed. Specifically, the removing mechanism of Pb(II) from aqueous solution via the synthesized zeolite involves two stages: one is that Pb(II) in aqueous solution is absorbed on the interior of the synthesized zeolite, and the other is chemical precipitation.

Study on the removal characteristics of different air pollution control devices for condensable particulate matter in coal-fired power plants.

This study reports the emissions of condensable particulate matter (CPM) and filterable particulate matter (FPM) in two coal-fired power plants with different air pollution control devices (APCDs). The mechanisms of CPM removed by existing APCDs in coal-fired power plants were explored, and a series of analyses were also carried out on the composition and characteristics of CPM. The results show that the removal efficiencies to CPM by electrostatic-bag-precipitator (EBP) and ESP are 77.34% and 79.23%, respectively, so the difference is not obvious because the interception filtration mechanisms of baghouses for CPM have less effect on CPM compared to FPM. The mechanism of EBP/ESP to remove CPM is mainly electrostatic adsorption and FPM's adsorption. The concentration of CPM decreases when passing through WFGD. However, the WESP can increase the CPM in different ways. For example, the pollution of the circulation of the flushing fluid may cause the increase of CPM. In addition, CPM mainly includes three parts. The first part is organic fractions such as alkanes and esters; the second is the water-soluble ions that include SO42-, NH4+, and Cl-; and the third is Na, Ca, and other minerals. The research in this study is helpful to understand the impact of existing APCDs in coal-fired power plants on CPM and the sources of CPM.

Transfer hydrogenation of CO2 into formaldehyde from aqueous glycerol heterogeneously catalyzed by Ru bound to LDH.

Aqueous glycerol was used in this study as a liquid-phase hydrogen source for the hydrogenation of CO2. It was found that hydrogen could be efficiently evolved from aqueous glycerol upon highly dispersed Ru on layered double hydroxide (LDH), inducing the transformation of CO2 into formaldehyde under base-free conditions at low temperature.

Mechanistic investigation of elemental mercury adsorption over silver-modified vanadium silicate: A DFT study.

Ag-modified vanadium silicate (EVS-Ag) has been regarded as a superior sorbent for elemental mercury (Hg0) capture from coal-fired flue gas. However, the atomic-level reaction mechanism which determines Hg0 adsorption capacity of EVS-Ag sorbent remains elusive. Reaction mechanism and active sites of Hg0 adsorption over EVS-Ag sorbent were studied using density functional theory (DFT) calculations systematically. DFT calculation results indicate that silver exchange shows little effects on the geometric structure of EVS-10 sorbent. Hg0 adsorption on EVS-10 and EVS-Ag surfaces is controlled by the physisorption and chemisorption mechanisms, respectively. Ag2 cluster is determined to be the most active site of Hg0 adsorption over Ag-modified EVS sorbent. The adsorption energy of Hg0 on Ag2 cluster is -51.93 kJ/mol. The orbital hybridization and electron sharing between Ag and Hg atoms are responsible for the strong interaction between EVS-Ag surface and Hg0. HgO prefers to adsorb on Ag2 cluster of EVS-Ag sorbent, and yields an energy release of 306.21 kJ/mol. HgO desorption from EVS-Ag sorbent surface needs a higher external energy, and occurs at the relatively higher temperatures. O2 molecule promotes Hg0 adsorption over EVS-Ag sorbent. HgO species can be easily formed during Hg0 adsorption over EVS-Ag sorbent in the presence of O2.

A novel light scattering method with size analysis and correction for on-line measurement of particulate matter concentration.

Based on the difference in particle size sensitivity between forward and backscattering during the measurement of particulate matter (PM) mass concentration using laser angular scattering, a method was proposed to improve its on-line measurement accuracy using three fixed detectors. Experimental and theoretical calculations indicate that the PM mass concentration sensitivity (PMCS) of the particles at the 22.5° detection angle and the asymmetry factor (I45°/I135°) are linearly related to the average particle size, and both decrease as the particle size increases. The average particle size obtained from the asymmetry factor was used to correct the PMCS. Compared with the unmodified light scattering method, when the PM mass concentration varies in the range of 1-8 mg⋅m-3, the average deviation between the light scattering method with particle size correction and the reference is reduced from 191.11 % ± 9.12 % to 8.90 % ± 3.20 %, and the maximum deviation is reduced from 227.04 % to 21.54 %. The effect of particle size on the measurement is reduced by size analysis and correction, and the accuracy of the light scattering method is much improved. Finally, laboratory measurements of the fly ash from coal-fired and biomass-fired power plants were performed.

Effects of kaolin-limestone blended additive on the formation and emission of particulate matter: Field study on a 1000 MW coal-firing power station.

Effects of a blended additive made of kaolin and limestone on the formation and emission characteristics of particulate matter (PM) was discussed for the first time. Systemic characterizations on the concentration, size distribution, elemental composition, micromorphology, specific resistivity of the PM were performed. Results revealed that the blended additive diminished the mass concentrations of the ultrafine PM and PM2.5 out of the furnace by 29.77 % and 40.91 % respectively. Interestingly, the additive also significantly reduced coarse PM, with the reduction efficiency for PM in 0.3-1 µm of ∼43 %. The additive captured the mineral vapors and thereby suppressed their migration into the ultrafine PM. Well, interactions among additive and ash promoted melting of the additive/ash particles. This improved the scavenging of both ultrafine and coarse PM via the liquidus capture mechanism. After the electrostatic precipitators (ESPs), emission of the ultrafine PM slightly increased after adding the additive because of the increasing of the specific resistivity of the ash particles and the reduction of electronegative gas (e.g., SO2) in the ESPs. The emission of total PM2.5 decreased by 32.31 % as less fly ash entering ESPs. Additionally, the leaching behaviours of heavy metals Cr, Mn, As and Pb in the fly ash were investigated.

Vanadium silicate (EVS)-supported silver nanoparticles: A novel catalytic sorbent for elemental mercury removal from flue gas.

Vanadium silicate (EVS) is a vanadium-substituted form of titanosilicate that has a high potential for use as a sorbent for mercury removal. In the present study, EVS with supported silver nanoparticles (EVS-Ag100) as the catalytic sorbent was synthesized for elemental mercury (Hg°) capture. The physical and chemical properties of the sorbents were investigated. The raw EVS exhibited a poor Hg° capture capacity (7.7 µg g-1), because most of the vanadium species in the structure of EVS were V4+. The loading of the silver could significantly enhance the Hg° capture capacity (63.4 µg g-1). EVS-Ag100 exhibited a superior Hg° capture performance at temperatures of approximately 150 °C. Silver nanoparticles that formed on the EVS were the active sites. In addition, the vanadium species of EVS-Ag100 exhibited higher Hg° oxidation activity than those in the framework of raw EVS. The XPS results revealed the activation of the vanadium species by the silver nanoparticles. After the capture of Hg° in the presence of O2, more V5+ was observed on the surface of EVS-Ag100. Exposure of EVS-Ag100 to a continuous simulated flue gas at 150 °C with a gas hourly space velocity of 220,000 h-1 led to Hg° removal efficiency of >96% in a 1 h test.

Influences of In-Furnace Kaolin Addition on the Formation and Emission Characteristics of PM2.5 in a 1000 MW Coal-Fired Power Station.

The impacts of in-furnace kaolin addition on the formation and emission characteristics of PM2.5 from a 1000 MW coal-fired utility boiler equipped with electrostatic precipitators (ESPs) are investigated for the first time ever in this contribution. Detailed characterization of the chemical composition, micromorphology, melting characteristics of the fine PM, total fly ash, and/or bottom ash samples were carried out using the X-ray fluorescence probe, the field emission scanning electron microscope coupled with an energy dispersive X-ray detector, the ash fusion analyzer, and the dust specific resistivity analyzer. The results showed that the formation of fine PM was reduced when kaolin was added, and the mass concentrations of the particulate matter with the aerodynamic diameters of ≤0.3 and 2.5 µm (PM0.3 and PM2.5) were reduced by 55.97% and 5.48%, respectively. As expected, kaolin reacted with the volatile mineral vapors (e.g., Ca, Na) and inhibited their partitioning into ultrafine PM. It was interesting to find that the added kaolin modified the ash melting behavior, and promoted the capture of the ultrafine PM onto the coarse particles. What is more, the added kaolin reduced the specific resistivity of the fly ash and improved their capture efficiency in the ESPs. Finally, the above combined effects brought about the emission reductions of 41.27% and 36.72% for PM0.3 and PM2.5 after the ESPs. These results provided a direct confirmation on the feasibility of in-furnace kaolin addition on the PM reduction in the realistic combustion conditions.

Using the Novel Method of Nonthermal Plasma To Add Cl Active Sites on Activated Carbon for Removal of Mercury from Flue Gas.

A new method using nonthermal plasma to add Cl active sites on activated carbon was proposed to improve the efficiency of activated carbon (AC) for removal of mercury from flue gas. The experiments were conducted via a lab-scale dielectric barrier discharge nonthermal plasma system and a vertical adsorption reactor. The results showed that the nonthermal plasma treatment with a small amount of Cl2 successfully added Cl active sites on AC and greatly increased the mercury removal efficiency of AC by chemisorption in a very short treatment time. The increase in Cl2 concentration for AC treatment promoted the efficiency of AC. The capacity of mercury adsorption positively correlated with the content of Cl2 for AC treatment, which depends on the number of Cl active sites on activated carbon. The treated AC maintained a high mercury removal efficiency within a temperature range of 30-210 °C. SO2 and H2O in flue gas inhibited the removal of mercury by AC, while HCl had a promotional effect. Scanning electron microscopy and X-ray photoelectron spectroscopy analysis indicated the chemisorption of mercury was attributed to the C-Cl groups generated on AC surfaces during Cl2 nonthermal plasma treatment. The C-Cl groups as active sites had strong adsorption energy for mercury, which converted elemental mercury to HgCl2.

Alkali-Doped Lithium Orthosilicate Sorbents for Carbon Dioxide Capture.

New alkali-doped (Na2 CO3 and K2 CO3 ) Li4 SiO4 sorbents with excellent performance at low CO2 concentrations were synthesized. We speculate that alkali doping breaks the orderly arrangement of the Li4 SiO4 crystals, hence increasing its specific surface area and the number of pores. It was shown that 10 wt % Na2 CO3 and 5 wt % K2 CO3 are the optimal additive ratios for doped sorbents to attain the highest conversions. Moreover, under 15 vol % CO2 , the doped sorbents present clearly faster absorption rates and exhibit stable cyclic durability with impressive conversions of about 90 %, at least 20 % higher than that of non-doped Li4 SiO4 . The attained conversions are also 10 % higher than the reported highest conversion of 80 % on doped Li4 SiO4 . The performance of Li4 SiO4 is believed to be enhanced by the eutectic melt, and it is the first time that the existence of eutectic Li/Na or Li/K carbonate on doped sorbents when absorbing CO2 at high temperature is confirmed; this was done using systematical analysis combining differential scanning calorimetry with in situ powder X-ray diffraction.

Preparation of Novel Li4 SiO4 Sorbents with Superior Performance at Low CO2 Concentration.

This work produced Li4 SiO4 sorbents through an impregnated-suspension method to overcome its typical poor performance at low CO2 concentrations. A SiO2 colloidal solution and two different organic lithium precursors were selected. A bulgy surface morphology (and thus, the significantly enlarged reacting surface area) was obtained for Li4 SiO4 , which contributed to the high absorption capacity. As a result, the capacity in cyclic tests at 15 vol % CO2 was approximately 8 times higher than conventional Li4 SiO4 prepared through a solid-state reaction. The phenomenon of a progressively increasing capacity (i.e., sustainable usage) was observed over the 40 cycles investigated, and this increasing trend continued to the last cycle. Correspondingly, over the course of the multicycle absorption/ desorption processes, the sorbents evolve from lacking porosity to having a high number of micron-sized pores.

Synthesis of CaO-based sorbents for CO(2) capture by a spray-drying technique.

Highly effective and durable CO(2) sorbents were synthesized with different calcium and support precursors using a spray-drying technique. It was found that spray-drying could be a useful technique for producing sorbents with enhanced cyclic performance, especially when d-gluconic acids of calcium and magnesium were used. Seven sorbents were synthesized with five calcium precursors and three inert solid precursors, and the sorbent made from calcium d-gluconte monohydrate and magnesium d-gluconate hydrate with 75 wt % CaO content achieved a high CO(2) sorption capacity of 0.46 g of CO(2)/g of calcined sorbent at the 44th cycle of carbonation and calcination.

[Experimental study on emission characteristics of PM10 in coal-fired boilers].

Fly ash was sampled at the inlet and outlet of ash collectors in four different coal-fired utility boilers using 13-stage low pressure impactor (LPI). The mass distribution, emission characteristics and the composition at different size particle of PM10 were studied. The results show that PM10 of the four boilers have a similar himodal distribution, with two peaks formed around 0.1 microm and 2.36 - 3.95 microm, respectively. The lowest efficiency of ash collectors was between 50% - 65% when the particle sizes were around 0.1 - 1 microm, no matter Venturi water membrane dust collector or ESP was used. Ash collectors show different removal efficiencies to various particle sizes PM. The removal efficiency of ash collectors was about 96% around 10 microm, while under 1 microm it was between 62% - 83%. The chemical composition of the size-segregated ash showed that the element S and Na were obvious enrichment in finer ash, which is possibly formed via vaporization and subsequent condensation of inorganic matter. While the refractory oxides were the major composition in bigger size ash, which may be formed via char fragmentation, excluded mineral fragmentation and included mineral coalescence.

Influence of calcium chloride on the thermal behavior of heavy and alkali metals in sewage sludge incineration.

In order to separate and reuse heavy and alkali metals from flue gas during sewage sludge incineration, experiments were carried out in a pilot incinerator. The experimental results show that most of the heavy and alkali metals form condensed phase at temperature above 600 degrees C. With the addition of 5% calcium chloride into sewage sludge, the gas/solid transformation temperature of part of the metals (As, Cu, Mg and Na) is evidently decreased due to the formation of chloride, while calcium chloride seems to have no significant influence on Zn and P. Moreover, the mass fractions of some heavy and alkali metals in the collected fly ash are relatively high. For example, the mass fractions for Pb and Cu in the fly ash collected by the filter are 1.19% and 19.7%, respectively, which are well above those in lead and copper ores. In the case of adding 5% calcium chloride, the heavy and alkali metals can be divided into three groups based on their conversion temperature: Group A that includes Na, Zn, K, Mg and P, which are converted into condensed phase above 600 degrees C; Group B that includes Pb and Cu which solidify when the temperature is above 400 degrees C; and Group C that includes As, whose condensation temperature is as low as 300 degrees C.

Simulating the transformation of heavy metals during coal or sewage sludge combustion.

A mathematical model (FPM) is presented to predict the transformation of heavy metals in the downstream of combustor or incinerator. The model accounts for the transformation of heavy metals through the combined effect of condensation, nucleation, coagulation, external force and thermophoresis force. The calculation of heavy metals is embodied in the post-processor appended to Fluent soft. Before the simulation, velocity, temperature, PbCl2 concentration and other initial parameters are obtained by experiment. In addition, the transformation of PbCl2 is also experimentally studied. The comparison of experimental and predicted results indicate that the fine particle model (FPM) is valid for predicting the transformation of heavy metals in the downstream of incinerator or combustor.

Multi-Monte Carlo method for coagulation and condensation/evaporation in dispersed systems.

A new multi-Monte Carlo (MMC) method is promoted to consider general dynamic equation (GDE) for particle coagulation and condensation/evaporation. MMC method introduces the concept of a "weighted fictitious particle" and is based on time-driven Monte Carlo technique, constant number of fictitious particles technique, and constant volume technique. MMC method for independent coagulation, for independent condensation/evaporation, and for simultaneous coagulation and condensation/evaporation are validated by some special cases in which analytical solutions exist, in which numerical results agree with corresponding analytical solutions well. Furthermore, the computation cost of MMC method is low enough to be applied in engineering computation and general scientific quantitative analysis.