Assessment of coal and ash environmental impact with the use of gamma- and X-ray spectrometry

Gamma-ray spectrometry (GS), energy dispersive X-ray fluorescence (EDXRF) analysis methods and wavelength dispersive X-ray fluorescence (WDXRF) were applied for the studies of some coal components, e.g., sulphur, light and heavy metal element concentrations and naturally occurring radioactive isotope contents. Hundred fifty coal samples originating mostly from eight different coal mines from Upper Silesian Coal Basin and 150 samples of ash obtained from these coal samples in laboratory by total combustion at final temperature of 820°C, were analyzed. Such comparitive analyses can be helpful in selection of most suitable kind of coal for burning in electrical power and heat plants to minimize the environmental pollution.     

Thermogravimetric investigation on combustion characteristics of oil shale and high sulphur coal mixture

Co-combustion experiments of mixture of Huadian oil shale and Heshan coal with high sulphur content have been conducted using a thermogravimetric analyzer. The effects of five different Ca/S mol ratios on the combustion characteristics of mixture fuel are analyzed using TG and DTG curves. The results show that the initial temperature of combustion of mixture fuel is decreased with an increase in the oil shale content of mixture fuel. The combustion characteristic of mixture fuel is superior to that of Heshan coal. Adding about 20 mass% Huadian oil shale into Heshan coal is feasible for desulfurization of mixture fuel during combustion.     

新疆高钠煤中钠的赋存形态及其对燃烧过程的影响

采用不同萃取液对中国新疆高钠煤进行逐级萃取实验,利用离子色谱仪和电感耦合等离子体原子发射光谱仪对萃取制得的滤液和固体煤样进行相应的元素分析,并通过逐级萃取后煤样的着火温度、燃尽温度和综合燃烧特性指数来分析高钠煤中不同存在形式钠对其燃烧特性的影响.结果表明,中国新疆高钠煤中的钠主要以水溶钠为主,有机钠和不可溶钠含量较少.影响高钠煤中水溶钠含量的主要因素有煤颗粒内部孔隙结构和颗粒粒径,且高钠煤中有机钠在各个粒径范围都保持了相对稳定的含量.煤种不同会导致煤中水溶钠与水溶氯的存在形式不同.煤中水溶钠的存在不利于高钠煤的着火温度和燃尽温度的降低与燃烧特性的提高,相反煤中的有机钠却对其具有促进作用.     

不同灰化温度下生物质混煤灰的烧结特性研究

选取晋城无烟煤和麦秆作为研究对象,利用压差法烧结温度测定装置测量不同灰化温度下煤和麦秆混合灰的烧结温度,再利用SEM-EDS以及XRD对灰样进行烧结特性分析。结果表明,不论灰化温度高低,随着麦秆的添加,煤和麦秆混合灰的烧结温度都呈现降低趋势,其降低幅度略有差别。灰化温度较低时,煤和麦秆混合灰的烧结温度低于灰化温度较高情况下混合灰的烧结温度。SEM-EDS分析表明,低温灰化得到的样品中出现较多不规则的纤维结构;较高温度下获得的灰样中出现较多致密的球状颗粒,这表明矿物质发生熔融形成球状颗粒。XRD分析表明,低温灰化烧结后的煤和麦秆混合灰样中因含有较多的含钾等碱金属系助融矿物质,导致混合灰样的烧结温度降低。然而,像钙长石等含钙矿物质本身具有较高的熔点,因此,在1 100℃时混合灰样具有较高的烧结温度。     

煤燃烧中的汞转化模型和数值模拟

煤燃烧中汞高温下以单质形式存在，在烟道里随着温度降低，单质汞部分转化为二价汞，并再有部分汞吸附在灰渣中而被除尘设备收集，减少了环境的汞污染。针对煤燃烧汞的转化过程，用动力学模型和吸附模型结合来描述汞的转化机理，并用数值模拟方法研究了煤中氯的质量分数、烟气降温速率、烟气停留时间等因素的影响。结果表明，煤中氯的质量分数为0.08×10－6以上，烟气停留6s以上时，可以使汞的吸附率达到40％以上。对汞转化模型，用一组580MJ/h燃烧系统150℃烟道温度数据进行了验证，结果证实试验数据与计算数据能较好相符，模型具有一定的可靠性。     

Sulphur capturing by an inertinite rich high ash bituminous coal during conversion in a pilot packed bed reactor

Sulphur is liberated from the coal structure and released in various forms during coal thermal processing. The possibility of sulphur capture, through injection of SO₂ into a packed coal bed in a pilot packed bed reactor operated under controlled conditions, was investigated. Results showed that SO₂ injection into a packed coal bed leads to sulphur capturing mainly in the coal mineral matter. Mineralogical analysis (XRD) of the ash samples obtained from the experiments indicates that the sulphur-capture products that are formed include FeS, CaS and small amounts of organically associated sulphur. Troilite (FeS) was observed in the SO₂ treated samples, while no troilite was observed in the reference samples. Calcite and dolomite are transformed into CaO and other calcium-containing compounds in the pyrolyses zone, with some CaS being formed in the gasification zone via the reaction between SO₂ and CaO in the presence of CO from the gasification reactions. CaO formed at the high temperatures in the combustion and ash zone is transformed into CaSO₄ upon reaction with SO₂ as an oxidizing atmosphere prevails in this zone. The existence of these compounds is dependent on the extent of oxidising or reducing conditions during the process, with CaS favoured under reducing conditions and CaSO₄ favoured under oxidising conditions.     

旋流煤粉燃烧的一维综合数值模拟

发展了综合考虑气－固两相旋流流动，气相燃烧，颗粒相变与燃烧及两相辐射传热的旋流煤粉燃烧－维数学模型，给出了气－固两相能量方程中颗粒相就源项的计算表达式，应用这一模型对涡旋燃烧炉环形通道内多组工况的旋流气体燃烧和煤粉燃烧进行了数值模拟，计算得到的炉内温度分布和燃烧效率与实验数据基本相符，表明本文建立的模型可用于旋流煤粉燃烧的一维综合数值模拟。     

低阶煤程序升温热解过程中钠、硅和硫间的相互作用

对一种澳大利亚低阶煤中,钠、硅和硫在热解过程中的相互作用进行了研究,以便深入了解钠的固硫作用和硫对流化床燃烧和气化中颗粒团聚的影响。制备了水洗、酸洗煤样和酸洗、乙酸钠离子交换煤样,样品在马弗炉中以17．7℃／min升至1000℃进行程序升温热解。对700℃-100℃热解半焦样品的依次水洗、酸洗、SEM—EDX和X射线元素扫描分析表明,部分有机结合的钠形成水溶性Na2O和NaOH化合物,水溶性的硅酸钠,以及与半焦中的硫形成酸不溶组分。最后一点解释了为何以往研究中发现,热解过程中有机结合的钠具有固硫作用,以及固硫历程中为何未发现Na2S的生成。在硅酸钠区域边缘存在的高硫区域,在流化床燃烧和气化过程中将形成含硫黏性相,导致床料的黏结。当用于酸洗、钠离子交换煤样的乙酸钠从0．25mol／L增加到1．0mol／L,固硫率将增加10％。相应的酸不溶钠组分的增加表明,酸不溶钠／硫组分随乙酸钠浓度的增加而增加,从而导致固硫率上升。     

石油焦与煤混合燃料热重分析研究

石油焦与煤混合燃烧是高效处理石油焦的有效方法，作者对选用的石油焦和煤不同配比的混合燃料进行了热重分析研究。使用常压高温热天平研究、分析了各配比混合燃料的热解特性和燃烧特性。并根据化学动力学方法计算了各过程的化学动力学参数，即活化能E和频率因子A0。结果表明，各混合燃料热解起始温度大致相同，随煤焦比减小，挥发分析出速率变缓，最大释放速度所对应的温度升高，最终失重率减小，挥发分释放特性指数减小；随煤焦比增大，混合燃料着火温度和燃尽温度逐渐降低，最大燃烧速率所对应的温度降低，燃烧特性指数增大；随煤焦比减小，活化能和频率因子增大。     

循环流化床燃煤过程NO、N2O和SO2的排放行为研究

在30kW循环流化床装置上进行了中国西部三种煤的燃烧实验，考查了燃烧温度、空气分级、空气过剩系数、固体颗粒循环料率和煤种等因素对NO、N2O、SO2污染物排放的影响。结果表明，强化空气分级可显著降低高挥发分煤种NO的生成量，但对N2O影响不大；增加空气过剩系数同时增加了NO与N2O的排放；增加固体循环料率显著降低NO生成量，但N2O排放略有增加；高阶煤燃烧生成较多N2O，低阶煤生成较多NO。燃烧温度1120K、过剩空气系数1.25下约85%燃料中N转化为N。实验范围内改变操作参数不影响SO2与CO排放量。     

无机酸洗脱对胜利褐煤微晶结构及其自燃倾向性的影响

利用XRD、Raman、XPS和FT-IR表征技术,研究无机酸洗脱(HCl、H2SO4、HCl-HF)处理的胜利褐煤微晶结构的变化,采用自行设计的表面吸附仪-GC联用装置,对样品进行不同温度的低温脉冲氧化实验,考察了煤样在不同温度下氧吸附量的变化规律,通过低温脉冲氧吸附规律与TG/DTG和固定床燃烧实验关联,考察了煤样的自燃倾向。结果表明,无机酸洗脱对矿物质的脱除使得煤结构的有序度增加,石墨化程度提高,无机酸洗脱煤样与原煤相比吸氧量明显下降。随着吸附温度的升高,各煤样吸氧量明显增加,且随着脱除矿物质程度的增加,吸氧量呈减小的趋势,导致自燃倾向降低。     

煤液化残渣与褐煤混煤燃烧特性的实验研究

煤液化是提高煤炭资源利用率、减轻燃煤污染的有效途径[1].在煤液化工艺过程中,煤液化残渣的主体是由液化原料煤中未转化的煤有机体、无机矿物质以及外加的液化催化剂组成,是一种高炭、高灰和高硫的物质,在某些工艺中会占到液化原煤总量的30%左右,如此多的残渣量对液化过程的热效率和经济性所产生的影响是不可低估的[2].     

Transformation of alkali and alkaline-earth metals during coal oxy-fuel combustion in the presence of SO_2 and H_2O

The occurrence modes of alkali and alkaline-earth metals(AAEMs) in coal relate to their release behavior and ash formation during combustion. To better understand the transformation of AAEMs,the release behavior of water-soluble,HCl-soluble,HCl-insoluble AAEMs during Shenmu coal(SM coal) oxy-fuel combustion in the presence of SO2 and H2O in a drop-tube reactor was investigated through serial dissolution using H2O and HCl solutions. The results show that the release rates of AAEMs increase with an increase in temperature under the three atmospheres studied. The high release rates of Mg and Ca from SM coal are dependent on the high content of soluble Mg and Ca in SM coal. SO2 inhibits the release rates of AAEMs,while H2O promotes them. The effects of SO2 and H2O on the Na and K species are more evident than those on Mg and Ca species. All three types of AAEMs in coal can volatilize in the gas phase during coal combustion. The W-type AAEMs release excessively,whereas the release rates of I-type AAEMs are relatively lower. Different types of AAEM may interconvert through different pathways under certain conditions. Both SO2 and H2O promote the transformation reactions. The effect of SO2 was related to sulfate formation and the promotion by H2O occurs because of a decrease in the melting point of the solid as well as the reaction of H2O.     

煤燃烧过程中铍的迁移转化特性研究

通过热力学平衡模拟计算煤燃烧过程中铍的形态转化,采用高温真空管式炉进行含铍化合物与矿物的固固反应实验,以及富铍煤中加入添加剂的燃烧实验,通过X射线衍射仪(XRD)、X射线荧光探针(XRF)以及电感耦合等离子质谱仪(ICP-MS)揭示煤燃烧过程中铍的迁移转化规律。结果表明,模拟计算发现铍只与含铝化合物反应生成BeAl_2O_4和Be Al6O10,同时固固反应实验也印证了这一结论,但反应温度在1 000℃左右,明显高于模拟计算温度650℃。添加Al_2O_3的富铍煤在燃烧时,由于铍与Al_2O_3发生反应,铍的释放率明显降低,最高降低33%以上;添加了伊利石的富铍煤,由于伊利石与铍的反应温度高于Al_2O_3,其抑制作用弱于Al_2O_3;而高岭石由于与铍的反应温度过高,在高岭石与铍发生反应产生抑制效果之前,部分铍已经在燃烧过程中释放出去,因此,抑制效果最差。     

Combustion kinetics and structural features of bituminous coal before and after modification process

Coal modification process is becoming popular to be used to upgrade coal quality. The upgraded coal (semi-coke) can be utilized in ironmaking process. Thermogravimetry and DAEM were used to analyze the combustion kinetics of bituminous coal before and after modification in this study. To understand the factors influencing the combustion process, various advanced techniques including X-ray diffraction analysis, Raman spectroscopy and Fourier transform infrared spectroscopy were adopted to investigate the structural features of the combusted samples. The results showed that the coal aromaticity increases significantly with the side-chains and chain length reduced, while the matrix structure transforms to graphite-like structure after the modification process. Those structural changes lead to the decrease in coal reactivity, thus weakening the coal combustion performance.     

准东煤灰化过程中的矿物演变及矿物添加剂对其灰熔融特性的影响

利用低温灰化、高温灰化和X射线衍射物相分析相结合的方法对准东煤中矿物质在加热过程中的演变规律进行了研究。结果表明,准东煤中原始矿物质以方解石、高岭石为主,随着燃烧温度的升高,煤灰中矿物质最终生成了铁橄榄石、硅酸钙等。此外,向准东煤中掺加不同比例的高岭土和刚玉混合添加剂,发现随着SiO₂/Al₂O₃比值的降低,煤中生成了钙矾石、钙铝榴石等高熔点物质,准东煤的灰熔点逐步升高。     

Thermal analysis study of the effect of coal-burning additives on the combustion of coals

Thermal analysis is widely used in combustion research for both fundamental and practical investigations. Efficient combustion of coals in cement industry is very important and necessary. In this research, the effects of three coal-burning additives on burning behaviour of bituminous coal and anthracite were studied with the help of thermogravimetry (TG) and differential scanning calorimetric (DSC) analysis. The kinetic study was carried out and the results were presented. The results showed that the coal-burning additives especially LSZ can reduce the ignition temperature, increase the ignition index D _i, combustion ending index D _f and affect the activation energy of the coal samples studied. The coal-burning additives especially LSZ can improve coal combustion effectiveness.     

Devolatilisation characteristics of coal and biomass blends

The characterisation of the initial devolatilisation products could provide important information for understanding synergistic effects and subsequently the formation routes leading to toxic organic compounds and soot during co-combustion. Initial devolatilisation characteristics of the fuels have been characterised following co-pyrolysis experiments. This paper investigates the devolatilisation behaviour during co-pyrolysis of pinewood together with one of three coals of different rank, lignite or high-volatile bituminous of different origin. A range of pyrolysis experiments has been performed over a temperature range from 400 to 900 °C using pyrolysis–GC–MS (py–GC–MS) and thermogravimetric analysis (TGA). Larger scale batch pyrolysis experiments of the hv bituminous coal–pine mixture have been performed enabling collection of the evolved tars. These tars have then been characterised by GC–MS and size exclusion chromatography (SEC). For these batch pyrolysis tests, synergy (non-additive behaviour) was observed and the blend pyrolysis oil contained a decrease in aromatics and an increase in phenols than would be expected for additive behaviour. The molecular weight distributions of the evolved tars also show non-additive behaviour. For the TGA experiments, additive behaviour was seen for all the coal–pine blends studied. Similarly, no obvious synergy was observed by py–GC–MS for the bituminous coal–pine blends, or for model compound–coal and coal–biomass component blends. Non-additive combustion behaviour is not easily explained by studying devolatilisation because of the difficulty in replicating the conditions of temperature profile and residence time experienced by the volatiles. Thus, conflicting behaviour is exhibited depending upon pyrolysis technique.     

石灰石的孔隙结构特性及对固氟反应的影响

用三种石灰石为研究对象，应用高温管式炉、扫描电子显微镜和压汞仪对样品进行了一系列宏观与微观的对比实验，探讨了石灰石的孔隙结构特性及对固氟反应的影响。结果表明，通过扩大比表面积、增加孔隙率和减小粒径等途径可以改善石灰石的孔隙结构特性，提高钙基固氟剂高温下的利用率。     

Thermal characteristics of the combustion process of biomass and sewage sludge

The combustion of two kinds of biomass and sewage sludge was studied. The biomass fuels were wood biomass (pellets) and agriculture biomass (oat). The sewage sludge came from waste water treatment plant. The biomass and sludge percentage in blends with coal were 10 %. The studied materials were characterised in terms of their proximate and ultimate analysis and calorific value. The composition of the ash of the studied fuels was also carried out. The behaviour of studied fuels was investigated by thermogravimetric analysis (TG, DTG and DTA). The samples were heated from an ambient temperature up to 1,000 °C at a constant three rates: 10, 40 and 100 °C min^?1 in 40 mL min^?1 air flow. TG, DTG and DTA analysis showed differences between coal, biomass fuels and sewage sludge. 10 % addition of studied fuels to the mixture with coal changed its combustion profile in the case of sewage sludge addition. The combustion characteristics of fuel mixtures showed, respectively, qualitative summarise behaviour based on single fuels. Evolved gaseous products from the decomposition of studied samples were identified. This study showed that thermogravimetric analysis connected with mass spectrometry is useful techniques to investigate the combustion and co-combustion of biomass fuels, and sewage sludge, together with coal. Non-isothermal kinetic analysis was used to evaluate the Arrhenius activation energy and the pre-exponential factor. The kinetic parameters were calculated using Kissinger–Akahira–Sunose model.