煤质劣化对锅炉热量分配影响的机理分析

受能源供应紧张影响电厂经常燃用劣质煤,其主要特点是灰分、水分大而发热量低,以此特征为基础建立一种煤质劣化模型。利用炉内传热相似理论求解方法,以一300 MW燃煤机组炉膛结构设计为例分析了不同劣化程度的煤质对锅炉主要设计参数造成的影响。计算结果表明:随煤中水分和灰分增加单位辐射热量降低,并且水分的影响大于灰分;随煤灰分增加单位辐射热量与单位对流热量之比升高,但随水分增加而降低。高负荷时,随煤中水分和灰分增加炉膛出口烟温略微降低;低负荷时,随煤中灰分增加炉膛出口烟温略微降低,而随煤中水分增加略微升高。     

Performance analysis of jig for coal cleaning using 3D response surface methodology

Beneficiation of coal of -4.76 mm + 3 mm size fraction was investigated in a laboratory model Denver jig.Process variables were studied to analyze their effect on the performance of jig in terms of yield and ash content of clean coal. Three-factor three-level Box-Behnken design of experiments with response surface methodology(RSM) was employed to understand the performance behavior of jig. From the study, the bed height was found to be the most significant parameter affecting the yield and ash content of clean coal. It was possible to reduce the ash content from 24.32% in feed to an ash content of 16.55% in clean coal at 2 L/min water flow rate and 10 min jigging time. Influence of operating variables of the jig on responses was presented and discussed in 3D surface plots. The developed model was found to be significant within the range of parameters under investigation with correlation of co-efficient values as 0.99(yield) and 0.98(ash).     

Effects of clay and calcium ions on coal flotation

The microflotation of three single minerals, mixed coal–kaolinite and mixed coal–montmorillonite were examined to study the effects of clay and calcium ions on coal flotation. The results show that the ash content of flotation concentrate increases by 3% in the presence of clay minerals, and the ash content would further increase by 3% in co-presence of clay minerals and high concentration of Ca²⁺. Scanning electron microscope (SEM) images and elemental spectrum analysis indicate that fine clay particles that coat on the coal surface, which is called slime coating, can affect the coal flotation. The slime coating would be induced much more easily in the presence of Ca²⁺.     

Extraction of valuable metals from low-grade nickeliferous laterite ore by reduction roasting-ammonia leaching method

Nickel and cobalt were extracted from low-grade nickeliferous laterite ore using a reduction roasting-ammonia leaching method. The reduction roasting-ammonia leaching experimental tests were chiefly introduced, by which fine coal was used as a reductant. The results show that the optimum process conditions are confirmed as follows: in reduction roasting process, the mass fraction of reductant in the ore is 10%, roasting time is 120 min, roasting temperature is 1 023–1 073 K; in ammonia leaching process, the liquid-to-solid ratio is 4:1(mL/g), leaching temperature is 313 K, leaching time is 120 min, and concentration ratio of NH₃ to CO₂ is 90 g/L:60 g/L. Under the optimum conditions, leaching efficiencies of nickel and cobalt are 86.25% and 60.84%, respectively. Therefore, nickel and cobalt can be effectively reclaimed, and the leaching agent can be also recycled at room temperature and normal pressure.     

Lowering ash slagging and fouling tendency of high-alkali coal by hydrothermal pretreatment

High-alkali species in coal are notorious for causing ash slagging and fouling incidents. In this paper, four high-alkali coals were individually subject to hydrothermal pretreatment(HTP), within a batch-type autoclave at 300 °C for 1 h, and the treated coals were analyzed, along with the oxygen-containing functional groups determined by Fourier transform infrared spectrometer(FT-IR). Then the alkali species and other components in the coal ash were quantified by X-ray fluorescence(XRF) for evaluating the ash slagging and fouling tendency. Apart from this, FactSage was adopted to simulate the occurrence and transformation of alkali species during coal thermal conversion ending at various temperatures. The findings indicate that the treated coals are superior to the parent ones in terms of certain remarkable changes via HTP. The moisture, oxygen and sulfur of the hydrothermally treated coals decline obviously, while the calorific value rises sharply. HTP could reduce the alkali species to less than 2%(%, by weight, equivalent to Na_2 O in dry ash), with a maximum removal ratio of 88.9%, lowering the ash slagging and fouling tendency. The proposed mechanism of HTP was that the alkali species in coal matrix became released due to the breakage of the coal functional groups and micropores during HTP.     

Prediction of oxygen concentration and temperature distribution in loose coal based on BP neural network

An effective method for preventing spontaneous combustion of coal stockpiles on the ground is to control the air-flow in loose coal. In order to determine and predict accurately oxygen concentrations and temperatures within coal stockpiles, it is vital to obtain information of self-heating conditions and tendencies of spontaneous coal combustion. For laboratory conditions, we de-signed our own experimental equipment composed of a control-heating system, a coal column and an oxygen concentration and temperature monitoring system, for simulation of spontaneous combustion of block coal (13-25 ram) covered with fine coal (0-3 mm). A BP artificial neural network (ANN) with 150 training samples was gradually established over the course of our experiment. Heating time, relative position of measuring points, the ratio of fine coal thickness, artificial density, voidage and activation energy were selected as input variables and oxygen concentration and temperature of coal column as output variables. Then our trained network was applied to predict the trend on the untried experimental data. The results show that the oxygen concentration in the coal column could be reduced below the minimum still able to induce spontaneous combustion of coal-6% by covering the coal pile with fine coal, which would meet the requirement to prevent spontaneous combustion of coal stockpiles. Based on the predic-tion of this ANN, the average errors of oxygen concentration and temperature were respectively 0.5% and 7 ~C, which meet actual tolerances. The implementation of the method would provide a practical guide in understanding the course of self-heating and spontaneous combustion of coal stockpiles.     

The Mineral Transformation of Huainan Coal Ashes in Reducing Atmospheres

By using the advanced instrumentation of a Computer Controlled Scanning Electron Microscope （CCSEM）, X-ray diffraction （XRD） and X-ray fluorescence （XRF）, the ash composition and the mineral components of six typical Huainan coals of different origins were studied. The transformation of mineral matter at high temperatures was tracked by XRD in reducing conditions. The quartz phase decreased sharply and the anorthite content tended to increase at first and then decreased with increasing temperatures. The formed mullite phase reached a maximum at 1250 ℃ but showed a tendency of slow decline when the temperature was over 1250 ℃. The mullite formed in the heating process was the main reason of the high ash melting temperature of Huainan coals. Differences in peak intensity of mullite and anorthite reflected differences in phase concentration of the quenched slag fractions, which contributed to the differences in ash melting temperatures. The differences in the location of an mnorphous hump maximum indicated differences of glass types which may affect ash melting temperatures. For Huainan coal samples with relatively high ash melting tempera- tures, the intensity of the diffraction lines for mullite under reducing condition is high while for the samples with relatively low ash melting temperature the intensity for anorthite is high.     

成灰温度对生物质与煤混烧中灰熔融性的影响

燃料的灰熔融性对受热面的结渣起着关键作用.生物质与煤的灰熔融性测定借用煤的测定标准,难以真实评判灰的熔融特性.在不同成灰温度下,利用HR-3C灰熔融性测定仪,以稻秆、白杨木屑、稻壳和煤在不同配比下混合燃烧的灰分作为研究对象,研究了成灰温度对生物质与煤混合燃烧的熔融特性.研究表明:不同的成灰温度对生物质与煤混合燃料的灰熔融性特征参数有着明显的影响,根据生物质中无机元素的特性和实际锅炉燃烧情况,对生物质与煤混燃成灰方法,借用ASTM E1755-01规定的低温成灰标准更能够准确反应其灰的熔融性.     

神华配煤孔隙分形对燃烧特性的影响

利用氮气吸附仪、沉降炉、扫描电镜(SEM)和X-射线能谱仪(EDS)研究了动力配煤的孔隙分形结构对着火和燃烧特性的影响.对神华煤分别与准格尔煤和澳洲煤组成的配煤研究表明,配煤孔隙分形维数随单煤比例呈现出单调变化规律,并且与比表面积和比孔容积的变化规律基本一致.当神华配煤的分形维数由2.451增加到2.482和2.532时,着火温度由783 ℃降低到587 ℃和462 ℃,飞灰中碳的质量分数由3.62%减少到2.83%和1.83%,说明配煤的分形维数越大则越容易着火和燃尽.随着准格尔煤比例增加和神华煤比例减少,燃烧渣样中硅铝质量比减小且灰熔点提高,导致配煤的结渣程度明显减轻.     

300 MW无烟煤锅炉选择性催化还原系统积灰原因分析

无烟煤锅炉由于挥发分含量低,着火困难,所以设计过程中都采用了较高的燃烧温度,从而导致选择性催化还原系统入口NOx排放浓度较高,脱硝系统压力较大。设计过程中灰颗粒尺寸选型不合理、灰黏性偏高、系统安装结构不合理以及喷氨量偏大等问题是引起脱硝系统积灰堵塞的主要原因。通过对脱硝系统优化改造和提高喷氨调整的自动化程度等,可以有效缓解选择性催化还原系统的堵塞情况;通过计算氨氮摩尔比,可以对氨逃逸浓度的测量结果进行校核。     

新疆石煤料团流化床焙烧提钒试验研究

在一台小型流化床燃烧试验台上对新疆石煤料团进行了焙烧特性的试验,着重考察了焙烧温度、焙烧时间、流化风速、添加剂种类对焙烧成球率的影响,并对飞灰、底渣、床料进行收集采样,利用水浸、质量分数为2%的Na2CO3溶液、6%的H2SO4溶液、10%的H2SO4溶液对各种样品浸取提钒,研究了焙烧温度、焙烧时间、浸取方式对转浸率的影响.结果表明:采用水泥为添加剂,温度为930℃,焙烧时间为90min,采用质量分数为10%的H2SO4溶液酸浸,可得较高焙烧成球率和转浸率,钒总回收率约为55.1%,同时可有效回收石煤热能,用于产汽发电.     

利用XRD分析高温下淮南煤灰矿物质变化

利用X射线衍射分析四种淮南煤在不同温度下煤灰矿物组成变化。结果表明：淮南煤中主要晶体矿物有高岭石、石英、方解石、黄铁矿等,高岭石类矿物含量越高,煤灰熔点越高;方解石和黄铁矿含量越高,煤灰熔点越低。煤灰中主要晶体矿物有石英、硬石膏、赤铁矿等,硬石膏和赤铁矿含量越大煤灰熔点越低。随着温度的升高,煤灰中石英、硬石膏、赤铁矿等结晶矿物含量逐渐减少,生成新的矿物质,莫来石的生成是导致淮南煤灰熔点高的主要原因,钙长石起到降低煤灰灰熔点的作用。     

Leaching kinetics of acid-soluble Cr（VI） from chromite ore processing residue with hydrofluoric acid

Leaching kinetics of acid-soluble Cr(VI) in chromite ore processing residue (COPR) using hydrofluoric (HF) acid solution as a leaching agent was investigated for potential remediation of COPR with industrial waste water containing HF. The results show that HF can effectively destabilize the Cr(VI)-bearing minerals, resulting in the mobilization of Cr(VI) from COPR into the leachate. Particle size significantly influences the leaching of acid-soluble Cr(VI) from COPR, followed by leaching time, whereas the effects of HF concentration and leaching temperature are slight and the influence of stirring rate is negligible. The leaching process of acid-soluble Cr(VI) from COPR is controlled by the diffusion through the product layer. The apparent activation energy is 8.696 kJ/mol and the reaction orders with respect to HF concentration and particle size is 0.493 8 and −2.013 3, respectively.     

两种煤配煤降低淮南煤高灰熔融性温度的研究

通过两两配煤的方法,对高灰熔融性淮南煤与4种灰熔融性温度较低煤进行配加,可以显著降低淮南煤的高灰熔融性温度,基本符合Texaco气化炉液态排渣要求。配煤灰熔融性温度的变化不是两种单煤灰熔融性温度简单的加和关系,而是非线形的关系,这与灰熔融过程中结晶矿物形成的种类不同有关。通过X-衍射分析,初步探讨灰熔融性机理。     

基于网格搜索和支持向量机的灰熔点预测

为了预测混煤的灰熔点,采用支持向量机建立煤灰软化温度模型,模型将煤的灰成分作为输入量,煤的软化温度作为输出量,利用网格搜索寻优方法对支持向量机(SVM)模型的参数进行了优化,在设定的不同精度下分别获得模型的最优参数,利用优化后的模型对单煤和混煤的灰熔点进行了预测,并将不同精度下的预测结果与实验结果进行对比.煤灰软化温度模型设定精度为0.01时,单煤样本预测相对误差最小,其最大相对误差和平均相对误差分别为3.00%和0.48%;运用此模型对混煤预测的最大相对误差和平均相对误差分别为1.74%和0.62%.预测结果表明,经网格搜索优化后的支持向量机模型对煤灰熔点预测较精确.     

成灰温度对生物质与煤混烧中灰熔融性的影响

燃料的灰熔融性对受热面的结渣起着关键作用.生物质与煤的灰熔融性测定借用煤的测定标准,难以真实评判灰的熔融特性.在不同成灰温度下,利用HR-3C灰熔融性测定仪,以稻秆、白杨木屑、稻壳和煤在不同配比下混合燃烧的灰分作为研究对象,研究了成灰温度对生物质与煤混合燃烧的熔融特性.研究表明：不同的成灰温度对生物质与煤混合燃料的灰熔融性特征参数有着明显的影响,根据生物质中无机元素的特性和实际锅炉燃烧情况,对生物质与煤混燃成灰方法,借用ASTM E1755-01规定的低温成灰标准更能够准确反应其灰的熔融性.     

Determination of trace multi-elements in coal fly ash by inductively coupled plasma mass spectrometry

The contents of Cr, Cu, Ni, As, Cd and Pb in coal fly ash were determined by a high resolution inductively coupled plasma mass spectrometry method. The sample digestions were performed in closed microwave vessels with HNO3, HClO4 and HF. The optimum conditions for the determination were obtained. The applicability of the proposed method was validated by the analysis of coal fly ash reference material (NIST SRM 1633a). The results show that most of the spectral interferences can be avoided by measuring in the high resolution mode (maximum mass resolution R=9 000). The detection limit is from 0.05 to 0.21 μg/g, and the precision is fine with relative standard deviation less than 4.3%.     

Slagging characteristics of molten coal ash on silicon-aluminum combustion liners of boiler

In order to study the slagging characteristics of boiler combustion liners during pulverized coal stream combustion, the slag samples on the surface of combustion liner were investigated by X-ray diffractometry, scan electron microscopy and energy dispersive X-ray analysis, and the transformation characteristics of the compositions and crystal phases were studied. The results show that the size of slag granules decreases as the slagging temperature increases; the crystallinity of coal ash I reduces to about 48.6% when the temperature is increased up to 1 350 ℃, and that of the coal ash II reduces to about 65% when the temperature is increased up to 1 500 ℃; the encroachment of molten coal ash to the combustion liner is strengthened. At the same time, the diffusion and the segregation of the compositions in combustion liners have selectivity, which is in favor of enhancing the content of crystal phases, weakening the conglutination among molten slag compositions and combustion liner, and avoiding yielding big clinkers. But the diffusion of the compositions in combustion liners increases the porosity and decreases the mechanical intensity of combustion liner, and makes the slag encroachment to the liner become more serious.     

凤阳山矿区太原组和山西组煤质特征分析

基于煤岩测试和工业分析数据评价了凤阳山矿区太原组、山西组可采煤层煤质特征,探讨了可采煤层煤质特征与成煤环境的关系。结果表明：太原组煤层为低灰分（Ad）、低挥发分（Vdaf）、高硫分（St,d）之贫煤,山西组煤层为低灰分、低挥发分、低硫分之贫煤。从下到上煤层镜质组含量、挥发分、硫分含量降低。山西组和太原组煤层灰分含量均较低,但山西组煤层灰分含量变化较大,灰成分指数较高。山西组煤层硫成分以Sp,d、So,d为主,硫分明显低于太原组煤层。从下向上成煤环境从浅海、滨海过渡相向陆相演化,泥炭沼泽水介质也从咸水、半咸水向淡水演化,因此,相应煤层煤质特征也表现出垂直分带性。