CHEMICALLY IMPROVED LIMESTONES FOR FLUIDIZED BED COMBUSTION OF COAL†

Preparation is made of a group of four new chemically improved limestones (SO₂-sorbents) from reactants of 65% limestone, 25% fly ash, and 10% binder of either a ball clay or mixture of the clay with a small quantity of colloidal silica. Fabrication is by pan granulation followed by varying extents of calcination. Potential products in the sorbents are inferred from the phase diagram of the CaO(base)-SiO₂(acid)-Al₂O₃(acid) system. The sorbents show SO₂-sorbency up to 2.8-3.0 times that of limestone during coal combustions, evaluations by both thermogravimetry (TG) using the Rapid TG Method and a 6-inch fluidized bed combustion (FBC) unit. Linear correlation with nearly perfect fit of data points is obtained between a parameter for SO₂-sorption by evaluations from the Rapid TG Method and SO₂-decrease in emissions by evaluations via the FBC method. Other linear correlations indicate a trend of direct proportionality between SO₂-decrease and carbon-decrease in FBC emissions. A chemical mechanism is suggested in order to describe this simultaneous occurrence of SO₂-decrease and carbon-decrease in emissions from coal combustion.     

镁负载CaO基吸附剂捕集CO2性能及抗烧结机理

复合钙基吸附剂制备成本过高是限制其工业化应用的主要瓶颈问题。本文以不可溶的CaCO₃和Ca(OH)₂作为钙源,通过燃烧合成法制备钙镁复合吸附剂,在双固定床反应器上研究了其循环捕集CO₂性能。结果显示：制备得到的钙镁复合吸附剂具有更发达的孔隙结构,吸附剂表面Ca和Mg分散均匀,MgO均匀分布于CaO晶粒之间,有效提高了钙镁复合吸附剂的抗烧结特性,因此钙镁复合吸附剂循环反应过程中具有高捕集CO₂活性。以Ca(OH)₂作为钙源时,燃烧合成过程中Ca和Mg均匀同时析出,分散更加均匀,有效避免了CaCO₃作为钙源时Mg的团聚问题,因此得到的钙镁复合吸附剂循环捕集CO₂性能最优。最佳的Ca/Mg摩尔比为(8∶2)~(7.5∶2.5)。本研究以不可溶钙源制备得到高活性钙镁复合吸附剂,有效控制了吸附剂成本,具有更好的工程应用前景。     

Comparison of microwave and radiofrequency low-temperature ashing of coal using Fe Mössbauer spectroscopy of sulphur forms

Low-temperature ashing of coal was carried out by the normal radiofrequency method and a new microwave technique to compare the effects of the two procedures on the Fe-S compounds in coal. Results from ⁵⁷Fe Mössbauer spectroscopy and chemical analyses indicate that the microwave technique, like the normal LTA procedure, effectively ashes the coal without the oxidation of pyritic sulphur. Dehydration of iron sulphates and oxidation of Fe²⁺ to Fe³⁺ in sulphates occurs in both ashing procedures under the conditions tested, the sequence being FeS0₄.4H₂O → FeS0₄.H₂0→Fe³⁺. Dehydration is caused by sample heating rather than by reaction with the activated oxygen. The combination of the Mössbauer method and chemical analysis has allowed the determination of the recoilless fraction ratio f(sulphate)/f(pyrite) = 0.55 ±0.15, which puts the Mössbauer results on a more quantitative basis than before. This is thought to be the first quantitative work on coal and coal products that has accounted for differences in f-values for different Fe compounds.     

DECOMPOSITION BEHAVIOR AND MECHANISM OF CALCIUM SULFATE UNDER THE CONDITION OF O2/CO2 PULVERIZED COAL COMBUSTION

The decomposition behavior and mechanism of calcium sulfate in O₂/CO₂ pulverized coal combustion were studied in an entrained flow reactor. A reaction rate expression correlating the influence of various factors was proposed for CaS0₄ decomposition and it is able to predict CaS0₄ decomposition satisfactorily. Under the conditions investigated, the decomposition of CaS0₄ was found to be a regime of chemically controlled shrinking core reaction. A CO₂-rich atmosphere enhances CaSO₄ decomposition in absence of oxygen. CaSO₄ particles have catalytic effect on formation of CO from CO₂. A high SO₂ concentration inhibits CaSO₄ decomposition. The kinetics of CaSO₄decomposition has obvious dependence on experimental facilities and conditions, whereas the activation energy has much lower dependence. The kinetics derived in this work is more appropriate for investigating desulfurization in O₂/CO₂ pulverized coal combustion because an entrained flow reactor has a much closer condition to that in O₂/CO₂ pulverized coal combustion than a TGA.     

燃煤过程中CaO及钙基固氟剂对氟析出的控制

燃煤过程中CaO与HF反应生成CaF₂.在燃烧温度900 ℃时,CaO对煤中氟析出的抑制范围为12.2%～61.0%,平均为39.5%.CaO固氟最佳条件是：燃烧温度800～1000 ℃,停留时间5～10 min, Ca/S（摩尔比）为2.5～3.0.钙基固氟剂由钙基吸收剂和添加剂组成,主要经历钙基吸收剂的分解反应、CaO固氟反应及硅铝钙等化合物的复合反应而形成高温稳定的固氟产物.工业链条炉燃烧试验表明:钙基固氟剂在全预混添加方式下固氟率为54.0%～64.8%,平均为59.3%;在半预混半喷射两段添加方式下固氟率为72.5%～80.5%,平均为75.5%,明显高于全预混添加方式. CaO和钙基固氟剂的固氟效果与燃烧条件、燃烧方式及固氟剂的种类和成分有关.     

DYNAMIC ADSORPTION OF S02 ON ZEOLITE MOLECULAR SIEVES†

Sulfur dioxide is one of the major pollutants resulting from fuel combustion. Numerous dry, semi-dry and wet processes have been developed for pollution control of sulfur dioxide. Solid carbonates, natural and synthetic zeolites, ion exchange resins and carbon based sorbents are the most commonly used dry sorbents for sulfur dioxide removal

In this study, measurements of the adsorption properties of sulfur dioxide on zeolites were investigated. The adsorbents used in this work are 5A, 4A and AW300 type molecular sieve zeolites. Adsorption equilibrium parameters were determined from the pulse chromatographic response to injections of low concentrations of sulfur dioxide. The method of moments were used to evaluate the adsorption equilibrium parameters from pulse chromatographic experiments. Data, such as adsorption equilibrium constants or reaction rate parameters are essential in the design of adsorption systems or reactors in which sulfur dioxide is removed

The experiments were conducted in a temperature range of 523-718 K. The relatively strong adsorption properties of sulfur dioxide on zeolites necessitated the use of high carrier gas flow rates and subsequently non-isobaric operation. Non-isobaric pulse chromatography theory was found to describe accurately the adsorption trends." printpubdate="Adsorption equilibrium constants of S0₂ were found to decrease considerably with increasing temperature. It was also found out that adsorption of SO₂ on the adsorbents investigated were found to decrease in the order of AW300 ≤ 4A ≤ 5A. The adsorption equilibrium parameter of S0₂ on 5A was found as 11.78 at 673 K, whereas it has a value of 157.11 at 523 K. The adsorption equilibrium parameter of S0₂ on 4A zeolite was determined to be 8.63 at 718 K and 213.78 at 523 K.     

控制煤和油页岩燃烧排放SO2污染物的研究进展

本文从分析我国大气污染的特征入手，探讨了煤和油页岩资源的合理利用途径，进行了降低燃煤排放ＳＯ２的方法比较，评述了煤和油页岩流化床燃烧过程中硫释放和脱除研究的现状，指出有待深入研究的问题有：（１）灰分的自固硫；（２）煤和油页岩含水量对脱硫的影响；（３）挥发分燃烧的火焰能量对颗粒油页岩燃烧排放ＳＯ２的影响；（４）煤和油页岩燃烧过程中硫释放的机理和本征动力学；（５）石灰石中惰性杂质对固硫性能的作用。     

基于热重-质谱联用的煤粉富氧燃烧动力学及污染物生成特性

富氧燃烧是最具工业化前景的燃烧中碳捕集技术之一,为更深入掌握煤粉富氧燃烧的着火模式和污染物生成特性,本文构建了热重-质谱联用实验系统,以烟煤和无烟煤标准煤样为对象,针对3个不同的氧气体积分数：21%、30%和50%,研究了O₂/Ar和O₂/CO₂气氛下煤粉的富氧燃烧特性。结果表明,O₂/CO₂气氛下煤粉着火温度和燃尽温度均降低,燃烧速率提高,燃烧时间缩短;两种煤粉在O₂/Ar气氛下的燃烧都属于非均相着火,而富氧燃烧都属于均相着火模式;氧气体积分数在30%以上时,无烟煤O₂/CO₂燃烧的表观活化能明显低于O₂/Ar气氛,在相同工况下烟煤的表观活化能均低于无烟煤;O₂/CO₂气氛促进了CO和挥发分NO的逸出,生成温度均低于O₂/Ar气氛,CO会对NO起到还原作用。     

Catalytic properties and surface modification of hexaaluminate microcrystals for combustion catalyst

Spinel oxide (Mn₃0₄) surface layers were produced on hexaaluminate microcrystals by means of the air-oxidation process. The surface layer completely covered the basal plane of hexagonal facets as evident from HREM observation and CO₂ chemisorption measurement. The catalytic activity of as prepared Mn₃0₄/hexaaluminate composites for methane combustion was evaluated as functions of the Mn₃0₄loading and the metal composition of the spinel surface layer. It was revealed that the air oxidationderived composites showed the excellent specific activities superior to those of the corresponding Mn₃0₄/hexaaluminates prepared from the conventional evaporation-to-dryness process. Partial substitution of Fe for Mn of the surface layer was effective in enhancing combustion activity in a whole temperature range.     

SURFACE AREA FORMATION IN DRY FGD SORBENTS

Dry flue gas desulfurization (DFGD) technologies are being developed which require sorbents with high specific surface areas capable of large sulfur dioxide uptake. Specifically, novel methods of controlling S0₂ in a fiuidized bed absorber are being studied which will have the capability of isothermal operation at optimum temperature for S0₂ uptake with alkaline sorbents. This paper reports on a study of surface area development with respect to time for three sorbent materials (pure calcium carbonate, dolomitic limestone and pressure hydrated dolomitic limestone) undergoing thermal decomposition in the temperature range of 600-850°C (1100-1550°F). Two of these sorbents (calcium carbonate and dolomitic limestone) confirm observations made by others of a lag time between recrystalization of the product from the reactant and the development of the maximum surface area. A model is presented which predicts the surface area development by accounting for the surface area generated by thermal decomposition and the surface area lost due to sintering. The parameters necessary for the model were obtained from the experimental data. The ability of the model to predict the surface area change with respect to time is shown to be good for the conditions tested.     

Fe-Zn基废脱硫剂制备铁碳材料及其对废水微电解性能

以Fe-Zn基废脱硫剂、煤、Na ₂CO ₃为原料进行高温炭热还原反应,制备了铁碳材料,实现了Zn和S的分离,有望能实现废脱硫剂的综合利用。考察不同工艺条件（配比,温度,时间）对铁碳材料品质,Zn单质分离效率和Na ₂S的收率影响。结果表明： 反应温度≥900℃,煤∶废脱硫剂≥1,Na ₂CO ₃∶废脱硫剂≥1.5,反应时长≥2 h,Zn、S的分离回收效率可达到95%以上。且900℃制备的铁碳材料比表面高达193.6 m ²/g,介孔孔体积为0.028 cm ³/g,炭均匀附着于铁骨架。微电解-芬顿联用降解有机废水实验表明：仅微电解或微电解-芬顿联用（H ₂O ₂=COD=1500 mg/L）时,自制铁碳材料的稳定化学需氧量（COD）去除效率（41.78%、73.56%）都高于商业铁碳（8.43%、48.43%)。本文实验结果表明废脱硫剂与煤和碳酸钠混烧可实现废脱硫剂中Zn与S的分离回收,成功获得了比表面高、去除COD性能好的铁碳材料。     

高温下改性钙基吸附剂固定床反应器从烟气中捕捉二氧化碳(英文)

Four kinds of Ca-based sorbents were prepared by calcination and hydration reactions using different precursors: calcium hydroxide, calcium carbonate, calcium acetate monohydrate and calcium oxide. The CO2 absorption capacity of those sorbents was investigated in a fixed-bed reactor in the temperature range of 350-650℃. It was found that all of those sorbents showed higher capacity for CO2 absorption when the operating temperature higher than 450℃. The CaAc2-CaO sorbent showed the highest CO2 absorption capacity of 299mg·g-1. The morphology of those sorbents was examined by scanning electron microscope (SEM), and the changes of composition before and after carbonation were also determined by X-ray diffraction (XRD). Results indicated that those sorbents have the similar chemical compositions and crystalline phases before carbonation reaction [mainly Ca(OH)2], and CaCO3 is the main component after carbonation reaction. The SEM morphology shows clearly that the sorbent pores were filled with reaction products after carbonation reaction, and became much denser than before. The N2 adsorption-desorption isotherms indicated that the CaAc2-CaO and CaCO3-CaO sorbents have higher specific surface area, larger pore volume and appropriate pore size distribution than that of CaO-CaO and Ca(OH)2-CaO.     

富氧燃烧下水蒸气对矿物捕集铬的影响

通过沉降炉煤燃烧实验及动力学模拟研究了水蒸气对Cr转化行为的作用及水蒸气对矿物吸附剂捕集Cr的影响。研究表明,CaO及Fe₂O₃在空气及富氧燃烧下均能较好地捕获Cr蒸气,石灰石的作用远差于CaO及Fe₂O₃,高岭土无论空气还是富氧燃烧下对捕集Cr均无效果。动力学模拟表明H₂O促进Cr（Ⅲ）快速转化为高价Cr蒸气CrO（OH）₂、CrO₂（OH）及CrO₂（OH）₂。富氧燃烧下H₂O抑制了CaO与Cr的反应,但燃烧灰中六价铬化合物大量增加,特别是当H₂O与CaO同时存在时,灰中43%的铬为六价铬。水蒸气促进了Fe₂O₃捕集铬化合物使其固定在灰中。富氧燃烧下水蒸气促进Cr在煤灰中富集,随着H₂O浓度由8%升高至20%,灰中铬的富集率又下降,主要由于水蒸气对CaO捕集Cr的抑制作用。     

Kinetics of PdO combustion catalysis

The kinetics of the catalytic combustion of methane by supported palladium oxide catalysts (2 wt.-% Pd/La₂O₃·11A1₂O₃ and 5 wt.-%Pd/ γ-A1₂0₃ were examined for several oxygen partial pressure levels over the temperature range from 40–900°C using temperature-programmed reaction and slow ramp and hold temperature-time transient techniques. Combustion rates were measured by differential reaction in a fixed bed of powdered catalyst at lower temperatures (200–500°C). Also, by preparing the catalysts as thin (ca. 10 μm) coatings on an alumina tube and conducting the experiments with very high flows of dilute methane and oxygen in helium, the rate measurements were extended up to 900°C without significant contribution from gas phase reactions. The specific combustion activity of supported PdO shows a persistent hysteresis between 450 and 750°C, i.e., the rate of combustion between these temperature limits depends strongly on whether the catalyst is cooling from above 750°C or heating from below 450°C. This region is also notable for negative apparent activation energy in the rate of methane oxidation, i.e., the rate increases with decreasing temperature during reoxidation of the Pd metal and decreases with increasing temperature (especially with low oxygen partial pressure) prior to decomposition of the bulk oxide. Detailed time-temperature transient kinetic analyses were performed for supported PdO catalysts within the 450–750°C temperature range. The hysteresis in methane combustion rate is caused by a higher activation energy for reduction of oxygen chemisorbed on metallic Pd and by suppressed reoxidation of Pd metal relative to PdO decomposition.     

Novel hierarchical yolk-shell α-Ni(OH)2/Mn2O3 microspheres as high specific capacitance electrode materials for supercapacitors

For high performance supercapacitors, novel hierarchical yolk-shell a-Ni(OH)₂/Mn₂O₃ microspheres were controllably synthesized using a facile two-step method based on the solvothermal treatment. The unique a-Ni(OH)₂ based yolk-shell microstructures decorated with numerous interconnected nanosheets and the hetero-composition features can synergistically enhance reactive site exposure and electron conduction within the microspheres, facilitate charge transfer between electrolyte and electrode materials, and release structural stress during OH⁻ chemisorption/desorption. Moreover, the Mn₂O₃ sediments distributed over the a-Ni(OH)₂ microspheres can serve as an effective protective layer for electrochemical reactions. Consequently, when tested in 1 mol·L⁻¹ KOH aqueous electrolyte for supercapacitors, the yolk-shell a-Ni(OH)₂/Mn₂O₃ microspheres exhibited a considerably high specific capacitance of 2228.6 F·g⁻¹ at 1 A·g⁻¹ and an impressive capacitance retention of 77.7% after 3000 cycles at 10 A·g⁻¹. The proposed a-Ni(OH)₂/Mn₂O₃ microspheres with hetero-composition and unique hierarchical yolk-shell microstructures are highly promising to be used as electrode materials in supercapacitors and other energy storage devices.     

A DRY SCRUBBING MODEL FOR SO2 REMOVAL

The use of dry injection of sorbents for control of S O₂ in conjunction with a fabric filter is currently undergoing evaluation at the large pilot plant level, and is being considered for full scale application. This paper discusses a recently developed model for predicting the removal efficiencies of S O₂ as a function of system operating parameters, and utilizing a semi-emperical pore plugging experience to account for the observed reaction die off behavior. The model assumes that the reaction between the gas and the solid occurs in two phases; (1) in a transport-line section where the finely powdered solid is injected and mixed with the flue gases, and (2) across the filter cake which develops at the fabric filter. In the current development of the model, isothermal conditions are assumed. Comparisons between predicted and reported values of S O₂ removal are given for the Na₂C0₃—S O₂ system     

燃煤砷污染和抑制的研究进展

对煤燃烧过程中微量砷的污染和抑制的国内外研究现状进行了综述 .概述了煤燃烧过程中微量砷的排放对环境产生的危害 .分析了煤中砷在燃烧过程中不同温度下的转化形态 ,烟气中砷的主要存在形态 ,以及煤中砷在燃烧产物中的配置和主要影响因素 .给出了美国不同电站的燃煤锅炉、工业燃煤锅炉以及民用燃煤锅炉砷的排放因子 .探讨了不同吸附剂与含砷化合物的作用机理 ,以及减少燃煤过程中砷污染的可行性 .强调了加强煤燃烧过程中微量砷排放研究的重要性     

粉煤灰浓硫酸焙烧过程及其非等温动力学

粉煤灰浓硫酸焙烧法提取Al₂O₃工艺中焙烧过程十分重要,研究发现适当提升硫酸浓度、酸灰质量比和温度可增大Al转化率,而延长焙烧时间影响并不显著;在硫酸浓度80%、酸灰质量比1.5:1、温度270℃和时间60 min条件下,Al转化率可达92 %～95%。TG/DSC与XRD分析表明,焙烧过程反应主要分为3个阶段:80～206℃时形成中间产物Al(HSO₄)₃及H₂O气化;206～241℃时生成Al(HSO₄)₃及Al₂(SO₄)₃·H₂O;241～304℃时由Al₂(SO₄)₃·H₂O和Al(HSO₄)₃二者分解转化成Al₂(SO₄)₃。由Kissinger微分法与Ozawa积分法分别计算出3个阶段表观活化能后取二者平均值,分别为52.61、74.11、96.08 kJ·mol^-1,并获得频率因子、反应级数和动力学方程,所获结果可为粉煤灰硫酸焙烧法提取Al₂O₃焙烧工艺设计和过程优化提供理论参考和基础数据。     

SIMPLIFIED DEWPOINT PREDICTIONS FOR N-TRACE SALT-CONTAINING NON-IDEAL CONDENSATES IN HIGH TEMPERATURE REACTIVE VAPOR ENVIRONMENTS

Accurate predictions of dewpoint temperatures in multi-trace salt-containing high temperature reactive environments are complicated by two common phenomena. First, the reactive environment promotes the formation of vapor precursors other than the 'parent' condensate salts (due to dissociation and reaction among the combustion products). Second, the salt condensate solutions that form are usually thermodynamically non-ideal even though the coexisting multi-species vapor is, frequently, ideal. As an extension of our recent treatment of the simpler (limiting) case of a binary non-ideal solution, we present here a computational procedure that makes the general N-component case tractable and illustrate its implementation for the case of a ternary (alkali sulfate) condensate system. To account for the multiplicity of vapor phase species we again rely on an 'effective (single component) vapor pressure' for each 'component' salt to permit simple calculations for the salt solution dew point. The required single salt vapor/liquid equilibrium data are here generated using a thermochemical equilibrium (free-energy minimization) code. When recast as an 'equivalent' vapor pressure correlation, this information is then used to solve the multisalt dewpoint problem by satisfying the requirements of vapor/condensate equilibrium with a multi-component non-ideal condensate solution. As an illustrative (ternary) case, using the principles outlined above, we carry out calculations for the prototypical system: K₂S0₄/Na₂S0₄/Li₂S0₄.     

TiO2掺杂对Na2CO3/Al2O3吸收剂CO2捕捉性能的影响

钠基固体吸收剂脱除燃煤烟气CO₂技术具有反应温度低、能耗低等优点,日益受到学术界的关注。该技术的主要不足是吸收剂的活性成分碳酸钠与CO₂的反应（碳酸化反应）活性较低。针对这一问题,本文旨在研制一种新型改性钠基固体吸收剂,采用活性氧化铝作为载体、TiO₂作为掺杂剂进行改性,利用热重分析装置、XRD、SEM和氮吸附仪研究钠基固体吸收剂的CO₂捕捉性能。结果表明：掺杂TiO₂后,钠基固体吸收剂与CO₂的反应速率加快,CO₂捕捉量增加;反应前后除TiO₂外无其他含Ti化合物生成;碳酸化反应产物为NaHCO₃和Na₅H₃（CO₃）₄;然而TiO₂掺杂过多会堵塞吸收剂的微观孔道,不利于甚至阻碍碳酸化反应的进行,因此,TiO₂的掺杂量应控制在一定的范围内。