Investigation on ash deposition characteristics during Zhundong coal combustion

The reserves of Zhundong (ZD) coal in China are huge. However, the high content of Na and Ca induces serious slagging and fouling problems. In this study, the ZD coal was burned in a DTF (drop tube furnace), and the ashes collected at different gas temperature with non-cooling probe were analyzed to obtain the ash particle properties and their combination mode. The results showed that Na, Ca and Fe are the main elements leading to slagging when the gas temperature is about 1000 °C during ZD coal combustion, but their mechanisms are quite different. Some sodium silicates and aluminosilicates and calcium sulfate keep molten state in the ashes collected at 1000 °C. These molten ash particles may impact and adhere on the bare tube surface, and then solidified quickly. With the growth of slag thickness, the depositing surface temperature is increased. The molten ash particles might form a layer of molten film, which could capture the other high fusion temperature particles. The Fe₂O₃ sphere were captured by the formed molten slag and then they blended together to form a new molten slag with lower melting temperature.     

Kinetics study for sodium transformation in supercritical water gasification of Zhundong coal

Zhundong coal (ZDC) has attracted much attention due to its high alkali metal content which can lead to a series of problems such as furnace slagging and ash fouling. Supercritical water gasification (SCWG) become a better choice for ZDC coal utilization because of its unique chemical and physical properties. The transformation mechanism of alkali metals during SCWG process was different from conventional ways of coal utilization. Systematic research about it could hardly be found. In this study, ZDC was used to explore sodium transformation mechanism and kinetics during supercritical water gasification under typical conditions. We got four kinds of sodium including the water-soluble fraction (L1), the carboxylic matrix-associated fraction (L2), the macromolecular organic group-associated fraction (L3), and the inorganic silicate mineral fraction (L4) through sequential extraction method after SCWG. A reaction pathway of sodium transformation in supercritical water gasification was proposed. A quantitative kinetic model for describing sodium transformation mechanism was developed. Finally, it was found that, L1 played an important role in catalytic process and mineral in coal weaken the catalytic process by combining with L1. L2 and L3 served as the two important intermediate products in the coal gasification, which explained the catalytic mechanism of sodium. L3 showed better reactivity. Sodium finally tended to deposit in the form of NaSiAlO₄ (L4) which was stable and environmentally friendly. All of these could provide basis for high-efficiency utilization of ZDC and the design of a reactor.     

Influences of sodium species with different occurrence modes on the thermal behaviors and gas evolution during pyrolysis of a sodium-rich Zhundong subbituminous coal

The Zhundong coal (ZDC) with a huge proven reserve is featured by high abundance of sodium species which behaves actively in the thermal conversion of it. In this work, to better understand the multiple roles of sodium species in coal pyrolysis, influences of sodium species with different occurrence modes on the thermal behaviors and gas evolution during pyrolysis of a sodium-rich ZDC were investigated. Raw coal was initially demineralized by dilute hydrochloric acid. Subsequently, sodium species was reloaded into the demineralized sample by ion-exchanged or immersed method. For quantitative analyses, a thermo-gravimetric analyzer coupled with a mass spectrometer was used to record the weight loss of different samples and the ever-changing amount of gaseous products in pyrolysis. The results show that the structural change induced by demineralized and ion-exchanged treatment is mainly reflected in the band intensity of carboxyl groups. In pyrolysis of ZDC, total volatile matters yield has a close relation with the occurrence modes of sodium species. It is proved that water-soluble sodium species has catalytic effects on the thermal-cracking reactions, whereas exchangeable sodium species tends to facilitate char-formed reactions. Compared with exchangeable ones, water-soluble sodium species can be also volatilized more easily in pyrolysis. As for gas evolution, exchangeable sodium species can obviously affect formation of CO through char gasification and it is also favorable to formation of hydrogen radicals. Moreover, due to the low sulfur content in ZDC, the intensity of H₂S released from all samples is extremely weak, which suggests that ZDC is a suitable feedstock for clean coal utilization.     

不同采矿深度准东煤物化特性和燃烧性能研究

选取天池能源浅层和深层煤样进行研究,以大同烟煤作为对比,了解采矿深度对煤质及燃烧特性的影响,为准东煤的勘探和燃烧提供必要的理论依据。研究发现,随着采矿深度的增加,煤中水分减少、灰分降低、发热量增加、含硫量减少,煤质更加接近烟煤;煤灰中Fe2O3明显减少,煤的结渣趋势减轻;煤的着火温度略有降低,燃烧速率提高,燃烧特性变好。与大同烟煤相比,准东煤高水分、低发热量、低氮含量,燃烧时着火温度显著降低且燃烧速率低。     

准东煤掺烧煤矸石安全性与经济性分析

高岭土与低钠煤可以有效抑制燃用准东煤时炉内的沾污结渣问题,但由于其价格升高,为降低电厂燃煤成本,因此提出将煤灰成分相似的煤矸石作为准东煤防结渣添加剂.分析煤矸石作为添加剂抑制炉内沾污结渣的可行性,根据入炉煤灰中折算Na2O含量低于3.0％,确定掺烧比例,并在某150 MW机组上进行实炉掺烧试验.通过掺烧试验分析可见,煤...     

降低循环流化床锅炉结渣风险的准东煤配煤掺烧研究

针对循环流化床锅炉燃用准东煤带来的受热面结渣和沾污问题,从降低入炉煤碱金属着手,采用准东五彩湾煤掺烧不同比例的煤矸石、低钠煤、沙漠黄沙,探究不同掺烧物料及比例对锅炉受热面结渣和沾污的影响。研究结果表明:掺烧25%煤矸石时,炉内受热面沾污、结渣严重,且存在频发的爆管现象;掺烧38%艾维尔沟低钠煤时,各级受热面均比较干净,没有明显的结渣沾污现象,但锅炉运行成本显著增加;掺烧5%古尔班通特沙漠黄沙时,仅在一级蒸发管高温烟区出现了类似于沙子的大焦块,其余受热面均比较光滑、干净,没有结渣和沾污现象。     

准东煤锅炉炉膛选型研究

研究了准东煤锅炉炉膛沾污系数和热负荷参数的选取,对进一步降低容积热负荷的可行性进行了探究。     

准东煤灰熔融特性试验研究

将神华准东煤（神华煤）和天池能源准东煤（天池煤）与碱沟煤按照不同质量掺混比进行混合并制得灰样,将NaCl、CaO、Al2O3和SiO2按不同添加比例加入神华煤和天池煤并制成灰样,对上述混合灰样的熔融特性进行研究.结果表明：碱沟煤掺混2种准东煤后,随着准东煤质量掺混比的增大,混合灰各个灰熔点特征温度先降低后升高;随着灰样中Na含量增加,准东煤灰样的变形温度显著降低,软化温度、半球温度和流动温度先降低后趋于不变;当灰样中Na含量达到一定比例后,NaCl对准东煤灰熔融特性的影响明显减弱;CaO对准东煤灰熔点的影响较复杂,可以降低也可以提高灰熔点;随着Al2O3添加比例的增加,准东煤灰熔点先升高后急剧降低;随着SiO2添加比例的增加,神华煤灰样的变形温度先升高后降低,而天池煤灰样的变形温度逐步升高,其他3个特征温度均逐渐降低.     

Hydrogen and syngas production from catalytic steam gasification of char derived from ion-exchangeable Na- and Ca-loaded coal

Catalytic steam gasification of char derived from low-rank coal possesses substantial potential as a source of hydrogen energy and syngas feedstocks, and its performances are largely associated with the employed catalysts. Therein, ion-exchangeable Na or Ca species are always regarded as excellent in-situ catalysts in low-rank coal. In this paper, gasification of Na-Char, Ca-Char and a Na/Ca-Char mixture with different partial pressures of steam was performed within a temperature range of 700–900 °C using a micro fluidized bed reaction analyzer. The results indicate that Na and Ca species could accelerate the gas release rate during gasification and even significantly increase H₂ production, in sharp contrast to non-catalytic gasification. Variations in the product gases during Na-Char and Ca-Char gasification were completely different, which associated with the different deactivation pathways and catalytic reaction mechanisms of Na and Ca catalysts. With an increasing gasification temperature, the decreasing trend of H₂ production for Na-Char gasification was mainly due to the loss of Na during gasification. Conversely, the enhancement of Ca activity promoted the H₂ production. The H₂/CO ratio of Ca-Char gasification at 700 °C approximately ranged from 1.0 to 2.0 as a function of the partial pressure of steam, which suggested catalytic gasification can be suitable for hydrogen-rich production and subsequent synthesis reactions. In addition, gasification of Na/Ca-Char mixture produced a higher hydrogen content in the product gases than that of Na-Char or Ca-Char gasification alone, particularly for the 30%Na/70%Ca-Char mixture. It implies that the high H₂ production of 70%Ca30%Na-Char mixture was attributed to the cooperative effects of the Na and Ca species on the catalytic activity. This study provides comprehensive information regarding the effects of ion-exchangeable Na, Ca and a Na/Ca mixture on the hydrogen production and syngas composition during steam gasification, which provides new insight into the utilization of low-rank coal.     

配煤对新疆准东高碱煤沾污结渣特性的影响

选用我国新疆准东地区某典型高碱煤和某低碱井工煤作为研究对象,研究了不同掺混比例对混煤灰熔融特性的影响,并应用相平衡理论对实验结果进行理论分析.结果表明:2种煤按不同比例混合后,由于混煤中的矿物质组成和煤灰化学成分发生变化,使得混煤灰的熔融特性也发生较大变化,混煤灰的熔融温度并不与2种煤的掺混比例呈线性变化关系,而与相应三元相图上的液相线温度具有一定的相似性;按照不同比例对不同煤样进行配比,可通过高温下煤中耐熔矿物质与助熔矿物质间的化学反应,改变混煤灰中的主要矿物质组成,减少高碱煤中Na、K等碱金属低温共熔物的生成,从而达到改变和调节煤灰熔融特性的目的.     

逐级萃取对准东煤的热解特性影响

为探究洗煤对准东煤热解特性的影响机理,采用逐级萃取法对准东煤进行洗煤处理。利用热重分析仪对比研究了洗煤对准东煤热解的影响规律,结合煤样热解前后样品的微观结构分析了洗煤对准东煤热解过程的作用机理,并采用分布活化能模型对煤样的热解反应动力学参数进行了计算。结果表明:脱除与煤中有机质结合的矿物质可以使煤样中产生大量新的多孔结构;洗煤会影响煤孔隙结构与官能团结构,导致煤样在热解初始阶段与热缩聚阶段失重量与失重率减少,主热解阶段失重量与失重率增大,并有利于煤焦微晶结构向石墨化进程演化;分布活化能模型可以较好地描述煤样的热解过程,随着洗煤程度的加深,活化能的分布曲线f(E)极大值对应的活化能由265.32升高至377.20 kJ/mol,说明热解反应活化能的主要分布区间向活化能较高的区域移动。     

Combustion performance and slagging characteristics during co-combustion of Zhundong coal and sludge

Zhundong coal (ZDc) with a very large reserve is faced with severe problems of slagging and fouling during combustion in boilers because of the high-Na content. Sludge, the by-product of urban sewage treatment, is also faced with the problem in utilization. In this study, the co-combustion of ZDc and sludge was investigated in a laboratory-scale experimental apparatus before further studies in larger-scale setups. The experimental results confirm an interaction between ZDc and sludge during co-combustion, which was mainly caused by the Na catalytic action and improved the combustion performance of the co-fuels. The catalytic effect was particularly significant at low sludge mixing ratios. The reactions between Na-based compounds in ZDc and Si/Al/P-rich minerals in sludge, forming high-melting-point phosphates and aluminosilicates, not only increased Na retention in residual ash reducing the risk of fouling on tail-heating surfaces in boilers, but also raised the ash fusibility of the co-fuels avoiding low-temperature sintering. Even so, to prevent slagging, the high combustion temperature above 900 °C should be avoided during co-combustion because of the high Na retention in residual ash. Moreover, the high heavy metal retention in residual ash decreased the pollution caused by heavy metal volatilization during sludge combustion.     

恒温下准东煤及其混煤燃烧过程中NO释放特性研究

基于恒温热重-燃烧污染物在线监测系统,通过对NO瞬时释放曲线的分析,并结合燃烧反应动力学计算,研究了恒温条件下燃烧环境温度对准东煤燃烧过程中NO释放特性的影响。结果表明：随温度升高,单煤和混煤燃烧过程中NO的释放时间会显著降低,释放速度显著提高;煤种成分的差异会导致NO释放特性的差异,固定碳挥发分的质量分数对NO释放有影响,而灰分的质量分数对NO释放无影响,当高固定碳、高挥发分的煤与低固定碳、低挥发分的煤进行掺混燃烧时,混煤的NO释放量和释放速率会降低。当燃烧过程中掺混北山煤时,混煤NO释放量低,释放速率慢,可以看作是一个较为优良的混煤掺烧方案。     

Chemical structure and pyrolysis characteristics of demineralized Zhundong Coal

To investigate the effects of acid treatments on the chemical structure and pyrolysis behavior of coal, we examined the low-rank Zhundong coal pretreated by four single acids (HCl, HF, H₂SO₄, HNO₃) and a combined acid (HCl-HF-HCl). Our results indicated that the carboxylic and phenolic hydroxyl contents of the coal increased, while the aliphatic and aromatic hydrogen contents decreased after leaching. Nitric acid destroyed long aliphatic chains in coal, which caused the key pyrolysis stage to occur at lower temperature, the number of volatiles increased, and the pyrolysis rate improved.     

准东煤与福建无烟煤燃烧特性的对比实验研究

通过对比准东煤与福建无烟煤的煤质分析、燃烧特性指数、燃烧动力学参数等,分析了准东煤与福建无烟煤的燃烧特性差异。结果表明：准东煤的挥发分明显高于福建无烟煤,属于极易着火的煤种;福建无烟煤与准东煤硫分低,燃烧中对环境污染小,但灰熔点都相对较低,容易结渣;准东煤的热重曲线较福建无烟煤向低温区偏移,峰区较宽,燃烧失重峰为双峰,着火方式由非均相着火向均相着火转变。准东煤的综合燃烧特性指数较大,表观活化能小;准东煤的煤反应活性和燃烧特性明显优于福建无烟煤。依热重分析,准东煤与福建无烟煤的着火温度分别为673.17 ℃和397.49 ℃,燃尽温度分别为803.05 ℃和741.18 ℃,活化能分别为191.39 kJ/mol和26.32 kJ/mol,综合燃烧特性指数分别为3.162×10-5和2.775×10-3。     

准东煤中钠元素赋存形态及洗煤对气化特性影响

为探究准东煤中钠元素赋存形态及洗煤对准东煤气化特性的影响,采用逐级洗煤法对准东煤进行洗煤处理。利用电感耦合等离子体质谱仪、离子色谱仪和X 射线衍射仪研究了准东煤中钠元素赋存形态及含量。利用热重分析仪研究了煤样的气化特性,并采用等转化率法计算气化反应动力学参数。结果表明：准东煤中钠元素主要以水溶钠为主,但并非以钠盐化合物晶体的形式存在于煤中。洗煤对煤样孔结构特性和矿物质含量均产生影响,矿物质含量较低时,气化特性主要由煤样的孔结构特性决定。随着洗煤程度加深,煤焦碳转化率达到90 %时所需的时间由5.35 min延长至12.02 min,气化反应活性指数逐渐降低,气化反应活化能由177.7～214.8 增大至203.5～252.4 kJ.mol-1。     

Effects of leaching and additives on the ash fusion characteristics of high-Na/Ca Zhundong coal

Considering the intensive application of Zhundong coal and its serious slagging during combustion in pulverized coal fired boilers, the effects of water leaching and different dosages of additives (Na₂CO₃, CaO, SiO₂, and kaolin) into the leached coal on ash fusion characteristics were studied using sintering tester, X-ray Fluorescence, and X Ray Powder Diffraction. After leaching, the contents of Na₂O, K₂O, CaO, MgO, SO₃, and Cl decreased, whereas the contents of SiO₂ and Fe₂O₃ increased. As a result, the slagging and fouling index of Basic/Acid ratio decreased from 1.6 in the raw coal ash to 1.1 in the leached coal ash, and alkali-induced slagging was reduced. However, the decreased ash fusion temperatures (AFTs) of the leached coal worsen the melt-induced slagging. Detailed analysis on the effects of ash compositions on the AFTs by additions of Na₂CO₃, CaO, SiO₂, and kaolin additives into the leached coal showed that Na₂CO₃ and SiO₂ improved the formation of low-melting Na₂SO₄ and Na₂SiO₃, and thus decreased the AFTs; However, overdosed Na₂CO₃ (for instance 9 wt%) improved the formation of relative high-melting Na₄Al₂Si₂O₉ and thus increased the AFTs. Overdosed SiO₂ as a high-melting contaminant also increased the AFTs. Similar with the function of overdosed SiO₂, CaO in the ash of leached coal was excess, and the AFTs increased with increased CaO dosage. Kaolin, which decomposed as high-melting mullite and cristobalite, caused an elevation of the AFTs. Therefore, water leaching decreased the AFTs of Zhundong coal and consequently worsen melt-induced slagging, lime and kaolin additives increased the AFTs effectively, but Na₂CO₃ and SiO₂ additives showed ‘V’ shaped functions on the AFTs. These general results are useful for the pretreatment of Zhundong coal during combustion and alleviating slagging.     

循环流化床锅炉纯烧准东煤吹灰器选型及应用研究

新疆某化工厂45 t/h循环流化床锅炉纯烧准东煤,省煤器积灰严重,导致排烟温度超过200 ℃。以该锅炉省煤器为研究对象,分析了省煤器积灰特征并选择气能激波吹灰器进行改造,对比了改造前后的排烟温度。研究表明：省煤器迎风面和背风面积灰为疏松多孔结构,积灰粒径范围在5~10 μm,呈椭球状或不规则球状,迎、背面灰分组成差异不大,主要由NaCl、MgO、CaSO4、CaCO3 和SiO2等组成,省煤器管束底层黏附的积灰难以清理;气能激波吹灰器对未沉积成型疏松性积灰有效,能大幅度改善省煤器换热效果,排烟温度下降了约40 ℃。     

羧酸钠对五彩湾煤热解及煤焦热反应性的影响

针对准东煤中高含量有机钠对煤热解燃烧会产生不利影响的问题,通过向酸洗脱除碱金属后的五彩湾煤定向加载羧酸钠的方法,对比分析加钠煤和再次脱钠二次酸洗煤的热重曲线、气体产物及不同温度热解焦在低温下的热反应性,研究羧酸钠对五彩湾煤热解和焦反应活性的影响。结果表明:羧酸钠会显著促进五彩湾煤热解挥发分的释放及煤羧基官能团的热分解,在600℃以下抑制CO的生成,600℃以上时则相反,同时高温下会抑制脂肪侧链的分解及煤的缩聚反应;羧酸钠对煤焦的热反应性具有催化作用,主要由两条路径实现:在煤焦表面形成\"C-O-Na\"基团或钠团簇进行催化。