Vapor-phase elemental mercury adsorption by residual carbon separated from fly ash

The adsorption capacity for vapor-phase elemental mercury(Hg0) of residual carbon separated from fly ash was studied in an attempt for the control of elemental mercury emissions from combustion processes. At low mercury concentrations(<200 μg/m3), unburned carbon had higher adsorption capacity than commercial activated carbon. The adsorbality of unburned carbon was also found to be source dependent. Isotherms of FS carbon(separated from fly ash of a power plant of Shishi in Fujian Province) were similar to those classified as typeⅡ. Isotherms of XJ carbon(separated from fly ash of a power plant of Jingcheng in Shanxi Province) were more like those classified as type Ⅲ. Due to the relatively low production costs, these residual carbons would likely be considerably more cost-effective for the full-scale removal of mercury from combustion flue gases than other technology.

Accelerated Carbonation Assessment of High-Volume Fly Ash Concrete

The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.

Analysis of Carbon Nanotubes Produced by Pyrolysis of Composite Film of Poly (Vinyl Alcohol) and Modified Fly Ash

We determined the catalytic function of chemically modified fly ash (MFA) for the growth of carbon nanotube (CNT) ropes with ~54% yield by the pyrolysis of the composite film of poly (vinyl alcohol) (PVA) at 500°C for 10 min under 2 L/min flow of nitrogen. Fly ash was treated with 2M sodium hydroxide to have MFA and used with PVA to fabricate the composite film by aqua casting. CNT was analyzed using SEM, TEM, XPS and Raman spectroscopy. The growths of CNT on MFA surfaces were visualized with different geometric self-assembly, e.g., bundles of CNT in ropes, twisted ropes, Y-branch ropes and staked-cone sheet. Thus, the mixtures of CNT ropes and MFA are a potential filler material for fabricating composites with polymer and metal.

Growth of Carbon Nanotubes by Pyrolysis of Composite Film of Poly (Vinyl Alcohol) and Modified Fly Ash

We found carbon nanotube (CNT) materials by the pyrolysis of the composite film of poly (vinyl alcohol) (PVA) reinforced with modified fly ash (FA) at 500°C for 10 min under 2 L/min flow of nitrogen. Fly ash was treated with 2M sodium hydroxide and used with PVA to fabricate the composite film by aqua casting. CNT materials were analyzed using XPS, Raman, SEM and TEM. The admixtures of CNT materials and FA are a potential filler material for fabricating composites with polymer and metal. The process is an eco-friendly recycling paradigm for using value-added advanced products for the proper management of sustainable waste materials, plastic and FA.

Characterization of LDPE Reinforced with Calcium Carbonate—Fly Ash Hybrid Filler

The synergetic effect of calcium carbonate (CC)-fly ash (FA) hybrid filler particles on the mechanical and physical properties of low density polyethylene (LDPE) has been investigated. Low density polyethylene is filled with varying weight percentages of FA and CC using melt casting. Composites are characterized for mechanical, thermal, microstructural and physical properties. Results show that the flexural strength increases with increases in FA content of the hybrid filler. It is evident from the study that to achieve optimum density a certain combination of both fillers need to be used. The optimum combination of CC and FA for a higher density (1.78 g/cm3) is found to be at 20 wt% FA and 30 wt% CC. An increase of 7.27% in micro-hardness over virgin polyethylene is obtained in composites with 10 wt% FA and 40 wt% CC. The presence of higher amount of CC is seen to be detrimental to the crystallinity of composites. X-ray, FTIR and DSC results show that composite with 45 wt% CC and 5 wt% FA exhibits a typical triclinic polyethylene structure indicating that the composite is amorphous in nature. There was the synergy between FA and CC fillers on flexural strength and crystallinity of composite. However, the fillers show the antagonistic effect on energy at peak and micro-hardness.

The Influence of Rice Husk Ash on Mechanical Properties of the Mortar and Concrete: A Critical Review

Increasing the population and infrastructure in both emerging and developed countries requires a considerable amount of cement, which significantly affects the environment. The primary materials of concrete (‘cement’) production emit a large quantity of CO2 into the environment. Also, the cost of conventional building materials like cement gives motivation to find geopolymer waste materials for concrete. To reduce harmful effects on the environment and cost of traditional concrete substance, alternative waste materials like rice husk ash (RHA), ground granulated blast-furnace (GGBS), fly ash (FA), and metakaolin (MK) can be used due to their pozzolanic behavior. RHA waste material with a high silica concentration obtained from burning rice husks can possibly be used as a supplementary cementitious material (SCM) in the manufacturing of concrete, and its strong pozzolanic properties can contribute to the strength and impermeability of concrete. This review paper highlights a summary of the positive effect of using RHA as a partial substitute for cement in building construction, as well as its optimal inclusion of enhanced mechanical properties like compressive strength, flexural strength, and split tensile strength of mortar and concrete.

脱除氢气流中AsH_3和PH_3的专用浸渍活性炭及滤毒罐(英文)

在半导体领域的金属有机物化学气相沉积 (MOCVD)过程中 ,排出含有剧毒AsH3 和PH3 的氢气 ,必须经过治理达标才能放空。为此 ,在从瑞典引进的MOCVD装置VP5 0 RP中 ,配套使用了德国DragerB3P3滤毒罐。研制出一种新型四元浸渍活性炭及滤毒罐 ,其在同等条件下对氢气流中AsH3 和PH3 的脱除能力为DragerB3P3罐的2倍～ 3倍。

Effects of Carbonation and Freeze-thaw Cycles on Microstructure of Concrete

The hydraulic concrete durability under the alternation of freeze-thaw and carbonation has been systematically investigated in this work, where both the micro part and the microscopic characteristics of concrete interface were analyzed based on computed tomography（CT） test and scanning electron microscopy（SEM）. Average CT numbers of each section, declined at water-cement ratio of 0.35, increased at 0.45, and changed a little at 0.55. The specimen in the absence of fly ash exhibited less types of hydration products and the surface was observed to be a needle-like ettringite, with a relatively dense overall structure. However, with the increase of fly ash content, pores and micro-cracks of specimen structure increased. Hexagonal flake calcium hydroxide, present in the specimen after the first carbonation, was negligible in the test pieces of the first freezethaw where the main hydration products were ettringite and calcium silicate gel. Regular hexagonal plates of calcium hydroxide exhibited in the interior of the specimen in which charring first occurred but calcium hydroxide rarely existed in the interior of the specimen in which freeze-thaw first occurred.

Comparisons of Fly Ash and Deposition Between Air and Oxy-Fuel Combustion in Bench-Scale Fluidized Bed with Limestone Addition

In Oxy-fuel circulating fluidized bed,the residual Ca O particles may react with high concentration of CO2 in flue gas to form bonded deposit on heat transfer surfaces in backpass when limestone is used as a sorbent to capture SO2.In this paper,experiments were designed on ash deposition in a bench-scale fluidized bed under oxy-fuel and air atmosphere. A novel ash deposit sampling probe was used to simulate the tubes of tail surfaces.The chemical composition of fly ash and ash deposit from both air-firing and oxy-fuel firing cases were analyzed by Inductively Coupled Plasma-Atomic Emission Spectrometry( ICP-AES) and Scanning Electron Microscopy( SEM),respectively. The degrees of carbonation reaction of ash deposits were measured by Thermo Gravimetric Analysis. The results showed that there are distinct differences in fly ash deposition rate between oxy-fuel and air firing cases,and oxy-fuel combustion with limestone addition can affect chemical composition of fly ash and ash deposit,especially for elements of Ca,Na,K,and S. However,the carbonation reaction degree of ash deposits is found weak,which is due to the relatively low Ca O content in ash deposit or not long enough of the sampling time.

Effect of activated carbon and electrolyte on properties of supercapacitor

Effect of activated carbon and electrolyte on electrochemical properties of organic supercapacitor was investigated. The results show that specific surface area and mesoporosity of activated carbon influence specific capacitance. If specific surface area is larger and mesoporosity is higher, the specific capacitance will become bigger. Specific surface area influences resistance of carbon electrode and consequently influences power property and pore size distribution. If specific surface area is smaller and mesoporosity is higher, the power property will become better. Ash influences leakage current and electrochemical cycling stability. If ash content is lower, the performance will become better. The properties of supercapacitor highly depend on the electrolyte. The compatibility of electrolyte and activated carbon is a determining factor of supercapacitor’s working voltage. LiPF6/(EC+EMC+DMC) is inappropriate for double layer capacitor. MeEt3NPF4/PC has higher specific capacitance than Et4NPF4/PC because methyl’s electronegativity value is lower than ethyl and MeEt3N+ has more positive charges and stronger polarizability than Et4N+ when an ethyl is substituted by methyl.

Toughness Improvement of Geothermal Well Cement at up to 300^&deg;C: Using Carbon Microfiber

This study aimed at assessing the usefulness of carbon microfiber (CMF) in improving the compressive-toughness of sodium metasilicate-activated calcium aluminate/Class F fly ash foamed cement at hydrothermal temperatures of up to 300&deg;C. When the CMFs came in contact with a pore solution of cement, their surfaces underwent alkali-caused oxidation, leading to the formation of metal (Na, Ca, Al)-complexed carboxylate groups. The extent of this oxidation was enhanced by the temperature increase, corresponding to the incorporation of more oxidation derivatives at higher temperatures. Although micro-probe examinations did not show any defects in the fibers, the enhanced oxidation engendered shrinkage of the interlayer spacing between the C-basal planes in CMFs, and a decline in their thermal stability. On the other hand, the complexed carboxylate groups present on the surfaces of oxidized fibers played a pivotal role in improving the adherence of fibers to the cement matrix. Such fiber/cement interfacial bonds contributed significantly to the excellent bridging effect of fibers, resistance to the cracks development and propagation, and to improvement of the post-crack material ductility. Consequently, the compressive toughness of the 85&deg;-, 200&deg;-, and 300&deg;C-autoclaved foamed cements reinforced with 10 wt% CMF was 2.4-, 2.9-, and 3.1-fold higher than for cement without the reinforcement.

Comparison of Prairie and Eroded Agricultural Lands on Soil Organic Carbon Retention (South Dakota)

The primary objective of this research was to predict changes in soil organic carbon (SOC) and total soil nitrogen (TSN) stocks as a result of land use change from prairie to agricultural land if the mesic-frigid temperature line moved north in the US and the former frigid soils were cultivated. The conversion of prairie to agricultural use, as a result of climate shift, would release SOC to atmosphere and enhance greenhouse gas emissions. The SOC and TSN differences between the prairie site and agricultural land were compared in South Dakota. The agricultural land had 18% less SOC and 16% less TSN or only half of the expected loss from prairie levels. An attempt was made to document the land use history of the prairie site to understand why SOC and TSN losses were less than anticipated. The fly ash concentration levels on prairie side slopes suggested that the prairie was historically disturbed and eroded. Intensive grazing and burning contributed to the disturbance. The SOC and TSN stock losses appear to represent the minimal change that would occur in the next 100-year time period if a prairie was shifted to agricultural use as a result of climate shift and the mesic-frigid temperature line in US was to move north.

Dry Mix Slag—High-Calcium Fly Ash Binder. Part One: Hydration and Mechanical Properties

High-calcium fly ash (HCFA)—a residue of high-temperature coal combustion at thermal power plants, in combination with sodium carbonate presents an effective hardening activator of ground granulated blast-furnace slag (GGBFS). Substitution of 10% - 30% of GGBFS by HCFA and premixing of 1% - 3% Na2CO3 to this dry binary binder was discovered to give mortar compression strength of 10 - 30 to 30 - 45 MPa at 7 and 28 days when moist cured at ambient temperature. High-calcium fly ash produced from low-temperature combustion of fuel, like in circulating fluidized bed technology, reacts with water readily and is itself a good hardening activator for GGBFS, so introduction of Na2CO3 into such mix has no noticeable effect on the mortar strength. However, low-temperature HCFA has higher water demand, and the strength of mortar is compromised by this factor. As of today, our research is still ongoing, and we expect to publish more data on different aspects of durability of proposed GGBFS-HCFA binder later.

飞灰含碳在线测量在660 MW机组锅炉燃烧中应用

针对失重法飞灰测碳装置在取样及测量方面的不足,利用防堵耐磨等技术提高飞灰测碳装置的测量精度和取样稳定性,并将装置应用于660 MW机组锅炉智慧燃烧系统中,通过精准飞灰含碳测量反映炉内燃烧状态,确保燃烧优化控制模型预测的正确性。研究结果表明,飞灰含碳实际值与预测值误差保持在较小范围内,最大误差不超过0.015%。优化燃烧系统后的现场运行结果表明,飞灰含碳量均值由2.1%降到1.5%,锅炉效率平均提高0.21%。

Bond Durability of Carbon-Microfiber-Reinforced Alkali-Activated High-Temperature Cement Adhering to Carbon Steel

The study aims at evaluating the bond durability of a carbon microfiber (CMF)-reinforced alkali-activating calcium aluminate cement (CAC)/fly ash F (FAF) blend cementitious material adhering to carbon steel (CS) under stresses induced by a 350℃ heat-25℃ water cooling cycle. This cementitious material/CS joint sample was originally prepared in an autoclave at 300℃ under a pressure of 8.3 MPa. For comparison, two reference geothermal well cements, Class G modified with silica (G) and calciumaluminum phosphate (CaP), were employed as well reinforced with CMF. In the CAC/FAF blending cement systems, the CAC-derived cementitious reaction products preferentially adhered to CS surfaces, rather than that of FAF-related reaction products. CMF played a pivotal role in creating tough interfacial bond structure of cement layer adhering to CS. The bond toughness also was supported by the crystalline cementitious reaction products including sodalite, brownmillerite, and hedenbergite as major phases, and aragonite, boehmite, and garronite as minor ones. The brownmillerite as an interfacial reaction product between cement and CS promoted the chemical bonding of the cement to CS, while the other phases served in providing the attractive bonding of the cement to CS. The post-stress-test joint samples revealed the formation of additional brown-millerite, aragonite, and garronite, in particular brownmillerite as the major one. The combination of chemical bonding and self-advancing adherence behavior of the cement was essential for creating a better interfacial bond structure. A similar interfacial bond structure was observed with CaP. The crystalline phase composition of the autoclaved cement revealed apatite, zeolite, and ferrowyllieite as major reaction products, and aragonite and al-katoite as the minor ones. Ferrowyllieite was identified as cement/CS interfacial reaction product contributing to the chemical bond of cement, while the other phases aided in providing the attractive bond of cement. After a stress test, two phases, ferrowyllieite and aragonite, promoted the self-advancing adherence of cement to CS. However, the effectiveness of these phases in improving adherence performance of cement was less than that of CAC/FAF blend cement, reflecting the fact that the bond durability of CAC/FAF blend cement was far better than that of the CaP. In contrast, the autoclaved silica-modified G cement consisting of xonotlite, and 0.9 nm-to-bermorite and riversideite, with calcite as the crystalline reaction products, had no significant effect on improving the shear bond strength and the bond’s toughness. No interaction product with CS was found in the cement adhering to CS. After a stress test, the calcite phase acted only to promote the self-advancing adherence of cement, but its extent was minimal compared with that of the other cements, thereby resulting in poor bond durability.

超声空化-流体剪切协同强化油团聚分选煤气化细渣

煤气化细渣(CGFS)具有较高的利用价值,但残炭回收率低极大地制约了其资源化利用。油团聚分选法在CGFS分选过程中具有明显优势,但炭灰共生结构严重限制了油团聚分选效率。为突破油团聚法分离富集残炭技术的瓶颈问题,考察了超声时间、超声功率、流体剪切时间及其交互作用对油团聚分选效果的影响,并结合BET、粒度分布、FT-IR、XPS以及SEM-EDS等分析手段,揭示了超声空化-流体剪切(UC-FS)协同预处理对油团聚分选效果的强化机理。结果表明:当超声功率为270 W、超声处理时间29 min、流体剪切时间23 min时,能分选得到灰分为9.55%的精矿、灰分为91.51%的尾矿,可燃体回收率可提高至90.54%。超声空化作用使原本致密的炭灰结构逐渐松散,与流体剪切的冲刷作用协同促进CGFS的孔隙结构的发展,使炭灰颗粒解离度增加,从而降低了精矿灰分。UC-FS协同预处理能够有效增加残炭表面C—C、C=C以及C—H等疏水基团的比例,使其接触角由110.34°增加到121.16°,扩大了炭和灰颗粒表面疏水性差异,提高了油团聚分选的效果。UC-FS协同预处理使炭灰颗粒高效分离的强化作用主要归因于超声空化气泡与细粒微球耦合产生的微磨料效应。可为实现CGFS分质资源化利用提供理论基础和技术指导。

基于高效解离-选择性絮凝耦合作用的煤气化渣提炭实验研究

煤气化渣是由煤气化工艺产生的一种富含铝硅酸盐、灰组分及残炭的大宗工业固体废弃物,其规模化生产对生态环境造成了严重的影响。因此,将煤气化渣进行炭-灰分离是实现其减量化、无害化和资源化利用的关键。以煤气化渣为研究对象,采用高效解离-选择性絮凝耦合作用的工艺,为实现煤气化渣更为合理、高效的资源化利用,减少煤气化渣带来的土壤、空气、水体资源等污染问题,对煤气化渣进行提炭实验研究。首先分析了煤气化渣的理化性质,其次采用单因素变量法探究了磨矿时间、pH、絮凝剂种类、絮凝剂用量、高速剪切转速对煤气化渣提炭实验的影响,以实现残余炭产品的高度富集。结果表明:原煤气化渣灰分质量分数为67.19%,普通湿筛筛上物料灰分质量分数为54.3%,当煤气化渣磨矿时间为5 s, pH为7,絮凝剂聚氧化乙烯用量为0.4 kg/t,在转速为4 000 r/min高速剪切15 min的条件下提炭效果最佳,最终可获得产率为26.6%、湿筛筛上灰分质量分数为43.3%的残炭产品。对比普通湿筛法,基于高效解离-选择性絮凝实验方法在普通湿筛的基础上灰分质量分数降低了11%,降灰效果明显。

碳纳米纤维混凝土抗盐-冻性能研究

为研究碳纳米纤维混凝土在盐-冻融循环作用下的抗冻性能变化规律,以3.5%NaCl溶液作为冻融循环介质,对4种不同碳纳米纤维(CNFs)质量掺量(0%、0.1%、0.2%、0.3%)的混凝土试件进行快速冻融循环试验,通过扫描电镜、X射线衍射和氮气吸附等微观测试手段分析纤维改性机理,并建立冻融损伤模型以评价盐-冻融循环条件下碳纳米纤维混凝土的损伤演化规律。结果表明,CNFs可提高混凝土抗盐-冻性能,改善效果与碳纳米纤维掺量呈正相关,质量掺量为0.3%时抗冻等级及耐久性指数较基准组提高100%。CNFs通过桥接裂缝、控制纳米级裂纹、成核、改善孔结构提高混凝土密实度,进而改善混凝土的抗盐-冻性能。基于不同评价指标建立的冻融损伤模型符合威布尔分布且R2均大于0.9,可用于评价和预测盐-冻融循环条件下碳纳米纤维混凝土损伤情况。

蔗渣灰基修补砂浆的经济性能环境影响的综合评价研究

为了开发用于复杂服役环境下混凝土受损结构的低碳修补砂浆,研究了不同掺量的蔗渣灰对修补砂浆的力学性能和抗氯盐侵蚀性的影响规律,对不同配比蔗渣灰修补砂浆的单位强度经济成本、单位强度碳排放、单位服役寿命碳排放3项指标进行分析,基于灰色聚类评估法对蔗渣灰修补砂浆的经济、性能和环境的影响程度进行评价。结果表明:考虑蔗渣灰修补砂浆处于潮汐浪溅区且保护层厚度为80 mm时,蔗渣灰掺量质量分数为15%的BA15蔗渣灰砂浆的服役寿命增长最大为213 a,相较于普通砂浆的103 a提高了106.7%,并且BA15蔗渣灰砂浆表现出最优异的经济成本和环境指标,在长期服役条件下的环境影响具有明显优势,相较于普通砂浆,其单位强度经济成本降低了18.8%,单位强度碳排放量降低了22.4%,单位服役寿命碳排放量降低了142.7%。基于灰色聚类评估法可知,蔗渣灰砂浆单位服役寿命碳排放的组合权重最大,通过提高蔗渣灰修补砂浆的服役寿命可以最大程度减轻砂浆碳排放造成的环境影响。建立了蔗渣灰基修补砂浆的综合评价模型,BA15蔗渣灰砂浆的综合评价指数K s最大为8.57,表现出最优异的综合评价。应控制蔗渣灰掺量质量分数在20%内才能使蔗渣灰修补砂浆的经济性能环境综合评价优于普通砂浆。

飞灰基吸附剂脱除烟气中Hg^(0)的研究进展

与其他脱汞方法相比,利用飞灰脱除Hg^(0)能降低脱除成本、实现以废治废。目前飞灰脱汞技术在工业应用中存在脱汞效率较低的问题,所以通过深入研究来提高其应用水平具有实际意义。归纳了飞灰结构和成分(有机、无机)对Hg^(0)脱除的影响机制。从提高脱汞效率角度,梳理了4种主流的飞灰改性方法:1)卤化物浸渍改性。卤化物在飞灰表面生成Br^(*)或与飞灰中未燃烧碳反应生成C-Br以氧化Hg^(0)。改性剂中的金属阳离子以加速电荷转移、降低反应能垒的方式来促进Hg^(0)的脱除。2)机械化学改性。该方法的制备工艺简单、成本低。飞灰经机械研磨使粒径减小后,无定形相及吸附氧含量增加。研磨后未燃烧碳充分暴露,卤化点位增加,加速了C-Br氧化Hg^(0)的进程。3)过渡金属改性磁珠。经过渡金属改性磁珠的磁性增强,可循环利用,使吸附剂表面引入新的Hg^(0)氧化位点(如C-O基团、Cl^(*))。4)低温等离子体改性。飞灰经低温等离子体处理后,吸附剂表面活性等离子体(如O、Cl等离子体)含量及官能团(C=O基团和酯基)含量增加,促进了Hg^(0)的吸附。进一步探究了复杂烟气组分对飞灰基吸附剂脱汞效率的影响,并对改性飞灰的脱汞性能及适用条件进行了评价。基于当前的研究进展,建议用磁性金属硫化物对飞灰进行机械化学改性来制备脱汞剂。