准东煤及其混煤燃烧与结渣特性

准东煤田是我国目前最大的整装煤田,煤质总体呈现中高水分、中高挥发分、低灰、低硫、低磷、中等热值、反应活性好等特点,是大规模煤化工、煤电气联产优质原料。但准东煤中较高的Na、Ca含量影响锅炉正常运行,限制了准东高钠煤的燃烧利用,目前电厂主要通过掺烧低钠煤方式加以利用。为考察准东煤及其混煤燃烧与结渣特性,在五彩湾电厂采集了准东煤(ZD)和乌东煤(WD)等2种原料煤。采用热重分析仪研究30%、50%和80%等不同配比下混煤燃烧特性,并分析响应配比下煤灰特性变化规律。结果表明,准东煤混煤燃烧的DTG曲线有2个特征峰。随准东煤配比增加,混煤燃烧TG和DTG曲线向低温区移动,DTG曲线特征峰更明显;混煤燃烧特征温度逐渐降低,最大燃烧速率与综合燃烧特性指数先降低后升高,混煤灰熔融温度逐渐降低。准东煤相对乌东煤具有较高的碱性氧化物和较低的酸性氧化物含量,准东煤配比越高相应的SO_3、CaO、Na_2O的含量越高结渣倾向性更强。但部分指标并不能准确预测结渣强弱,如准东煤硅铝比为1.67,而乌东煤硅铝比为3.02,依据硅铝比判断结渣倾向性与事实不吻合。另外,煤中CaO含量大于30%后继续增加则灰熔融温度升高,是准东煤比乌东煤具有更高灰熔融温度的原因,随准东煤配比增加,混煤灰熔融温度呈明显降低趋势。燃烧结渣与沾污倾向指标主要有基于煤灰成分和基于煤灰熔融温度的指标,总结分析以往结渣与沾污预测指标结合试验结果认为:基于煤灰成分的碱酸比以及基于煤灰熔融温度的特征温度差值(FT-DT)是判别准东煤及其混煤结渣与沾污倾向性的理想指标。     

O2/CO2气氛下烟气物性参数对燃煤锅炉对流传热影响的模拟研究

新疆准东煤作为一种可开发利用前景广阔的高碱金属煤种,易沾污结渣特性极大限制了其高效利用。前人大量研究了准东煤在常规气氛下的燃烧特性,但鲜见其在富氧气氛下的燃烧和传热特性研究。为了研究富氧气氛下燃用准东煤对碱金属释放及换热器传热性能的影响,运用化工流程分析软件Aspen Plus建立空气和富氧气氛下准东煤燃烧工艺流程模型并进行反应模拟。通过控制氧燃比恒定并调节O_2/CO_2配比进行变工况分析,使准东煤燃烧绝热火焰温度与空气气氛下较为接近,对应工况下锅炉内具有相似的温度分布。借助吉布斯反应器模拟得出反应物系在满足相平衡和化学平衡的条件下所得产物组分及状态参数、Na元素的赋存与转化规律,为预测Na元素释放形式提供参考。由于富氧燃烧烟气富含高浓度CO_2且水蒸气含量增加,富氧燃烧方式下燃煤烟气的传热特性将发生显著差异。运用带有Boston-Mathiasα函数的Peng-Robinson立方状态方程(PR-BM物性方法)对准东煤在空气和富氧气氛下燃烧产生的烟气进行物性估算,对比分析不同气氛下烟气密度、比热容、导热系数、黏度随温度的变化规律,为分析空气及富氧气氛下准东煤燃烧烟气的对流传热特性差异提供更为准确的参数。采用外掠管束强制对流传热修正计算方法分析了不同燃烧气氛下锅炉烟道内各对流受热面的传热性能。并采用CFD软件对一束高温再热器管屏进行"烟气-管壁-蒸汽"流固耦合传热数值模拟,对比空气及富氧气氛下燃煤烟气物性参数对换热器传热系数的影响。结果表明:40%O_2/60%CO_2气氛下,Na元素释放规律与21%O_2/79%N_2基本一致。随着烟温的降低,Na存在形式逐渐由NaCl和NaOH向Na2SO_4转变。但烟气再循环的富集作用会加剧准东煤灰沾污结渣。由于富氧燃煤烟气中三原子气体浓度增加,物性参数发生变化使得对流传热性能增强,各对流受热面传热系数为常规工况的1. 24～1. 27倍。在换热器结构和烟气及蒸汽入口流速、温度相同时,富氧工况下再热器各管圈对流传热系数较常规工况增加约21. 43 W/(m~2·K),出口蒸汽平均温度提高约11. 32 K。     

五彩湾煤在O2/CO2燃烧条件下的积灰特性

锅炉燃用准东煤极易发生严重的受热面积灰结渣等问题,制约了新疆准东地区煤炭资源的大规模利用。在一维沉降炉燃烧与积灰试验系统上,研究了准东五彩湾煤的积灰特性,分析了稀释气体种类、O_2/CO_2燃烧中氧浓度对飞灰沉积的影响。结果表明:在21%氧浓度下,与稀释气体为N_2相比,稀释气体为CO_2时得到的沉积灰颗粒之间黏连现象不明显,积灰倾向较弱; O_2/CO_2燃烧条件下,随着氧浓度提高,五彩湾煤的积灰倾向加重,细散灰颗粒减少,球形灰颗粒比例增加,灰颗粒的黏连现象加重。SEM-EDS分析结果表明:O_2/CO_2燃烧中随氧浓度的提高,沉积灰中的块状灰颗粒表面缩孔及凹坑增多,且灰颗粒表面黏附了白色细散絮状灰,Na和Cl的富集加重,这是造成高氧浓度燃烧受热面积灰加剧的重要原因;稀释气体种类对五彩湾煤积灰倾向的影响研究中,稀释气体为N_2(空气燃烧)时,Na和Cl含量明显高于稀释气体为CO_2(O_2/CO_2燃烧)时的含量。此外,燃烧稀释气体为N_2的沉积灰中还出现了Ca和S元素的富集,高温下CaO与硅铝酸盐发生反应生成低温共熔体,这也是空气燃烧时积灰较O_2/CO_2燃烧严重的重要原因。XRD分析结果在一定程度上佐证了EDS的分析结论,灰分中CaSO_4、NaCl等低熔点物质的富集导致了空气燃烧工况和O_2/CO_2高氧浓度燃烧工况积灰的加剧。燃烧的颗粒温度差异是导致O_2/CO_2燃烧和空气燃烧积灰特性不同的主要原因,也是造成不同氧浓度下O_2/CO_2燃烧积灰特性差异的主要原因。煤燃烧的颗粒温度较高时,煤粉着火、燃烧性能得到改善,更高的颗粒温度会导致烟气中出现更多的熔融灰,灰颗粒表面出现熔融相进而增强了灰表面的黏性,加剧积灰现象。     

准东煤燃烧过程中碱金属迁移规律

由于准东矿区地域宽阔,不同地区的准东煤性质存在一定差异。为了探求某准东煤的结渣沾污机理,在卧式管式炉及一维沉降炉中进行不同工况的准东煤燃烧试验,并通过电感耦合等离子体发射光谱仪对煤灰中碱及碱土金属含量进行表征,研究了准东煤在不同反应环境中碱及碱土金属的迁移和沉积规律。结果表明:随燃烧温度的升高,煤样中钠金属逃逸量升高,当温度超过1 100℃时,钠金属逃逸量为2 760μg/g,超过85%。不同温度下煤灰中相同种类的其他氧化物含量较接近,CaO与MgO在灰中占比较大。O_2体积分数对钠逃逸量的影响不明显,对相同种类氧化物占比影响较小,最大相差仅为0. 52%。在沉降炉试验中,随温度的升高,沉积灰灰样颜色由浅变深,灰沉积逐渐加重并难以清除,表明温度升高对结渣有促进作用。温度超过1 000℃时,Na挥发基本完成,含量稳定在11%左右。高温下,灰沉积管表面产生氧化皮脱落现象。在过量空气系数较大时,沉积灰灰样中的团聚烧结物较其他2种气氛少,但减弱幅度较小。炉膛中的煤粉燃烧均匀性随煤粉细度的增大而变差,导致部分煤粉剧烈燃烧使炉膛内局部温度偏高,灰沉积加重。此外,灰中的大颗粒数量也随粒径的增大而增多,黏结在结渣棒上的大颗粒增多。     

卧式液态排渣旋风炉燃烧高碱煤试验研究

我国新疆地区高碱煤储量巨大,但煤的原生矿物中含有大量Na、K等碱金属元素,导致目前新疆地区无法直接燃用该类煤种,许多电厂不得不掺烧其他煤种以满足锅炉正常运行,极大限制了其广泛利用。液态排渣旋风炉燃烧锅炉技术是一种使煤燃烧产生的大部分灰在旋风燃烧器内形成液态渣膜并从锅炉底部排出的锅炉技术,对于解决新疆高碱煤强沾污结渣问题具有一定优势。为研究液态排渣卧式旋风炉燃用新疆高碱煤液渣捕捉碱金属特性,在实验室条件下搭建液态排渣卧式旋风试验炉,并对新疆沙尔湖煤进行燃烧试验,对试验过程中在卧式液态排渣旋风试验炉内采集到的灰渣样进行SEM-EDS分析,根据其分析结果计算灰渣样中碱金属的固碱率,同时观察试验过程中炉膛内壁液渣的形成情况,测量炉内温度分布情况。结果表明:试验工况稳定后旋风炉内总体温度分布比较均匀,沙尔湖煤适用于液态排渣卧式旋风燃烧炉燃用,燃烧温度1 300℃时,旋风炉膛内开始形成液渣,升高燃烧温度,炉内液渣形成较为明显,卧式液态排渣旋风炉燃用高碱煤,炉内形成液渣时,液渣中Fe元素会黏结在硅铝酸盐颗粒表面,增加其黏性,加强烧结层捕获灰颗粒的能力,促进渣层生长;采用卧式液态排渣旋风炉燃用高碱煤能有效缓解炉膛内壁黏污、结渣问题,同时高温燃烧区相对于低温燃烧区缓解效果较为明显;卧式液态排渣旋风炉燃高碱煤时液渣对碱金属Na、K等的捕捉效率达50%以上,最高可达61.01%,高于自身固态灰、高温区添加高岭土对Na的捕捉效率。     

准东煤加压气化过程中Na迁移规律的热力学研究

准东煤中高含量的碱金属会在燃烧过程中引发严重的结渣与沾污问题,但准东煤气化过程中,在加压条件下碱金属的迁移转化规律仍不明确。为探究准东煤中NaCl在加压条件下的迁移转化机制,根据系统吉布斯自由能最小原则的热力学计算方法,采用HSC Chemistry的化学热力学平衡计算模块,对纯NaCl和准东煤中NaCl在加压过程中Na基化合物的物质的量进行计算。研究结果表明,压力显著影响纯NaCl的气化温度,在常压下,开始气化温度和气化完成温度分别为800℃和1 400℃;压力升至4 MPa时,气化开始温度和气化完成温度分别升至1 500℃和2 200℃。准东煤中Si、Al、H和O参与反应时,在0. 1 MPa条件下,300℃开始,NaCl逐渐与煤灰中的SiO_2、Al_2O_3和H_2O反应生成大量的NaAlSi_3O_8、NaAlSiO_4和Na_2SiO_3等Na基化合物。在1 500℃时,生成的气相NaCl仅占Na物质的量的25%左右。系统反应压力越高,生成低熔点且具有助熔作用的NaAlSi_3O_8、NaAlSiO_4、Na_2SiO_3就越多,导致炉内产生结渣的风险越高。     

碱金属和碱土金属对新疆准东煤利用的影响

阐述了准东煤具有低灰、低硫、中等热值、开采成本低以及反应活性高等优点，适用于燃烧、热解和气化等转化过程，是一种优质的动力煤和化工原料。然而，准东煤中钠和钙等碱金属和碱土金属含量较高，在燃烧过程中常会引发结渣、灰沉积等问题。总结了准东煤目前的利用情况，介绍了目前准东煤燃烧和气化过程中钠元素的迁移和释放过程及其所引发的结渣和积灰等问题，据此现状，研究人员提出了解决方法。针对现存问题，发现超临界水气化制氢技术可以有效解决准东煤的结渣堵塞等问题，超临界水气化将会是准东煤高效清洁利用的有效手段。     

离子交换法洗涤准东煤脱钠提质研究

针对新疆准东煤钠含量偏高,锅炉燃用时易发生水冷壁结渣、受热面高温腐蚀和烟道沾污积灰等情况,对准东煤的煤质特性进行分析,采用阳离子交换树脂洗涤准东煤,利用树脂的离子交换功能,使树脂的交换基团中的阳离子与准东煤的钠离子发生置换反应,达到脱钠的效果,并研究洗涤温度与洗涤时间对准东煤脱钠效果的影响.结果表明:在4h,60℃的恒温洗涤条件下,准东煤脱钠效果达到最佳,可溶性钠脱除率达到90%以上,t_s提高124℃,煤质特性得到改善.     

碱性氧化物对煤灰熔融特性影响的研究进展

准东煤中的钠、钙含量较高,导致在燃用过程中锅炉受热面发生严重的结渣。煤灰的结渣问题与煤灰的熔融特性密切相关,灰中碱性氧化物对灰熔融特性具有重要的影响。本文综述了碱性氧化物对煤灰熔融特性的影响。现有的研究表明,添加Na_2O可以显著降低灰熔融温度,钠长石、霞石等低熔点含钠矿物质的生成及其形成的低温共熔体是灰熔融温度降低的主要原因。灰中K_2O主要以伊利石的形式存在,对灰熔融温度的影响较小。随灰中CaO和MgO含量的增加,灰熔融温度具有先降低后升高的变化趋势,矿物质熔点的变化是灰熔融温度变化的主要原因。灰中Fe_2O_3的存在形式与反应气氛有关。在还原性气氛下,铁主要以FeO的形式存在,铁橄榄石、铁尖晶石等含铁矿物质容易形成低温共熔体,使灰熔融温度降低。未来应着重研究碱性氧化物对准东煤灰熔融特性影响的机理,开发抑制准东煤结渣的高效添加剂。     

高钠煤灰烧结特性研究进展

中国新疆准东煤具有储量巨大、开采成本低、挥发分高、硫含量低等特点,是优质的动力用煤。但准东煤钠含量高,燃烧利用时易在受热面上形成烧结性积灰,产生严重的结渣,极大限制了高钠煤的开发利用。因此,要实现高钠煤的清洁高效利用,需充分认识高钠煤灰的烧结特性。总结了高钠煤积灰结渣机理,概述了高钠煤灰烧结机制,探讨了二者之间的内在关联。高钠煤在燃烧过程中,煤中碱金属(主要为钠)释放并以Na_2SO_4、NaCl及Na的形式存在于烟气中,与受热面接触并于其上冷凝形成黏性内白层,内白层捕获飞灰颗粒后反应生成低熔点化合物,其烧结温度降低,使锅炉受热面上发生沾污增强型的"沾污烧结"过程。高钠煤灰的烧结过程包含固相烧结、液相烧结和气相烧结3种方式,对煤灰烧结过程的影响因素包括反应温度、化学组成、煤灰粒径、反应气氛、添加剂种类、锅炉设计和锅炉运行工况等。其中添加剂按氧化物种类可分为碱性氧化物和酸性氧化物,一般情况下碱性氧化物可以降低煤灰烧结温度,酸性氧化物可提高煤灰烧结温度。未来对于提高高钠煤灰烧结温度的研究方向可从新型添加剂出发,找到既能固定烟气中的钠,又能与灰渣中的低熔点含钠矿物质反应生成高熔点化合物的单一或混合成分的添加剂。同时,关于钠蒸气对积灰结渣在微观层面上的动态特性的影响机制也需进一步研究。概述了煤灰烧结温度的测量方法,热导率分析法、压力测量法、热机械分析法、筛分法和压降法,其中压降法是目前为止测量烧结温度较为准确的方法。介绍了上海理工大学碳基燃料洁净转化实验室在高钠煤灰烧结特性方面的研究方向,以期为解决燃用高钠煤锅炉积灰结渣问题提供参考。     

合成煤中钠对煤燃烧及灰特性影响

准东煤中钠含量高，燃用时锅炉会出现严重结渣问题。通过向准东煤为原料制取的超纯煤中添加灰的模型化合物，得到合成煤。并在此基础上利用热重-差示扫描量热分析法（TG/DTG/DSC）、X射线衍射仪（XRD）和灰熔融温度测定分析手段，研究Na₂O含量对煤燃烧特性和灰熔融性的影响。结果表明：钠主要影响合成煤的着火温度（T_i）与焦炭燃烧阶段，钠含量增加使T_i升高，并且Na₂O在灰中质量分数由5%升高至8%后，钠含量增加使焦炭燃烧速率先减小后加快，并能够改善煤粉燃尽特性。钠能够降低灰熔融温度，并在Na₂O质量分数高于5%后，温度下降更加明显。在三元相图中钠对莫来石的助熔作用是造成灰熔融温度降低的重要原因。XRD分析表明Na₂O含量增加，充当骨架作用的石英在钠的助熔作用下与难熔矿物硅钙石、MgO等生成低熔点长石类矿物，这类矿物在高温下有助熔作用，能够降低灰熔融温度。同时还生成助熔性含钠矿物霞石，加剧了灰熔融。     

Reducing fly ash deposition by pretreatment of brown coal: Effect of aluminium on ash character

The effect of pretreatment on the structure and the related fouling/slagging behaviour of fly ash from brown coal has been investigated. Condensable sodium salts and low melting sodium silicates are known as fouling and slagging materials. Experimental proof is given that less of such components were formed after treatment of Loy Yang brown coal with water and, particularly, with Al compounds.For the range of temperatures applied (1000–1400°C) in a drop tube furnace, the quantity of condensable salts generated was found to depend only on the amount of sodium in Loy Yang coal. Aluminium had the effect of reducing the sodium level by ion exchange and thus the formation of fouling ash components. The stickiness of sodium silicates from this coal was also shown to be reduced by aluminium.     

神华石炭-侏罗纪煤掺烧的结渣性能

神华侏罗纪煤具有易燃、低硫、低灰等优点,但存在易结渣等不足之处;神华石炭纪煤结渣特性则明显优于前者;侏罗纪煤与石炭煤掺烧,可充分利用石炭煤灰的高熔融温度特性以降低混煤的结渣倾向,并保持侏罗纪煤的易燃特性以提高混煤的火焰稳定性,具有低硫、低灰、较高热值、较低钙含量、低结渣、易燃烧等优点,保证了神华配煤在以非神华煤设计的锅炉中不会带来运行上的困难。笔者通过试验提出的神华两类煤掺烧结渣趋势变化图可为神华配煤方案的设计提供依据。     

Slagging and fouling characteristics of seam 32/33, Panian coalfield, Semirara Island, Philippines

Twenty samples of seam 32/33, the main seam of Panian coalfield in Semirara Island, Antique Province, Philippines, were collected from a borehole drilled at the northeastern edge of the coalfield. The samples were analyzed to characterize the coal geochemistry of the seam and understand why the coals of Semirara Island exhibit a high tendency for slagging and fouling despite its low average ash content. Analysis of the slagging and fouling characteristics of this seam is important because it supplies five electric power utilities and several cement plants in the Philippines. Proximate analyses and vitrinite reflectance measurements designate the rank of the seam as sub-bituminous C, based on ASTM coal classification. H/C versus O/C ratios indicate that the seam is made up largely of huminite, denoting early stages of coalification. Chemical analysis of the ash reveals high contents of Na, Mg, Fe, Ca, Ba and Sr. The strongly negative correlation of these elements with the ash content indicates an organic affinity of the chemical elements of the seam. Owing to enrichment in alkali and alkali-earth elements, slagging and fouling indices indicate that the seam has medium to high propensity for slagging and a severe tendency for fouling. The detrimental characteristics of coal feedstock from Panian mine is mitigated by modifications to the boiler design and operational conditions and by blending with coals imported from Indonesia, China and Australia.     

Ash deposition behavior of upgraded brown coal in pulverized coal combustion boiler

Ash with a low melting point causes slagging and fouling problems in pulverized coal combustion boilers. Ash deposition on heat exchanger tubes reduces the overall heat transfer coefficient due to its low thermal conductivity. The purpose of this study is to evaluate the ash deposition for Upgraded Brown Coal (UBC) and bituminous coal in a 145 MW practical coal combustion boiler. The UBC stands for Upgraded Brown Coal. The melting temperature of UBC ash is relatively lower than that of bituminous coal ashes. Combustion tests were conducted on blended coal consisting 20 wt.% of UBC and 80 wt.% of bituminous coal. Before actual ash deposition tests, the molten slag fractions in those coal ashes were estimated by means of chemical equilibrium calculations. The calculation results showed the molten slag fraction for UBC ash reached approximately 90% at 1523 K. However, that for blended coal ash decreased to 50%. These calculation results mean that blending UBC with bituminous coal played a role in decreasing the molten slag fraction. This phenomenon occurred because the coal blending led to the formation of alumino-silicates compounds as a solid phase. Next, ash deposition tests were conducted using a practical pulverized coal combustion boiler. A water-cooled stainless-steel tube was inserted in locations at both 1523 K and 1273 K in the boiler to measure the amount of ash deposits. The results showed that the mass of ash deposition for blended coal did not greatly increase, compared with that for bituminous coal alone. Therefore, appropriately blending UBC with bituminous coal enabled the use of UBC without any ash deposition problems in practical boilers.     

煤种性质对煤粉工业锅炉结焦的影响

燃煤锅炉内结焦会对锅炉运行的安全性和经济性造成极大损害,因而分析影响燃煤锅炉结焦的因素,进而有效预防燃煤锅炉结焦至关重要。在实际应用中,针对影响燃煤锅炉结焦的不同因素,可采取不同的预防措施。研究发现煤的灰熔融性温度、煤粉颗粒大小、锅炉燃烧气氛、一二次风动力场、锅炉截面热负荷和锅炉热负荷等都会影响燃煤锅炉结焦。为了解决某地区煤粉工业锅炉预燃室、炉膛、对流受热面大面积燃烧结焦问题,笔者结合燃煤锅炉燃烧结焦的机理,先后采取调整燃烧气氛、增大二次风刚性、减小煤粉颗粒粒径、更换孙家岔煤粉等措施对不同条件下的结焦现象进行对比分析,发现煤种、煤粉粒径大小是影响某地区煤粉工业锅炉燃烧结焦的因素。通过SEM-EDS(扫描电镜和能谱分析)对锅炉焦块进行微观形貌与元素组成分析,现场取样锅炉现用煤粉和孙家岔煤粉进行煤质及灰成分对比分析,并根据灰成分进行结渣性判别指标计算,结果表明锅炉燃烧现用煤种灰熔融性温度较低,煤灰软化温度Ts为1 170℃,小于1 200℃,为易熔煤,容易结渣,属于典型的易结焦煤种;结渣性判别指标计算结果显示,4项指标评价为"严重",1项指标评价为"中等",结渣性严重。综合分析认为:锅炉燃烧煤种发生改变,煤的灰熔融温度较低是影响某地区煤粉工业锅炉燃烧结焦的最本质因素。为进一步解决现场实际问题,采取破坏煤灰中酸碱平衡,提升煤的灰熔融温度,配合调节煤粉粒径等措施,如对锅炉现用煤种掺混5%的石英,提高煤灰中Si O2含量,掺混后煤粉的灰熔融温度达到1 280℃,提高了110℃;调大煤粉磨机频率,从19 Hz增大到22 Hz,煤粉粒度(200目,0.075 mm)过筛率从70%增大到85%。经过上述调整后,锅炉运行平稳,结焦状况显著改善,燃烧调整措施取得了较好的效果。     

Experimental investigation on the combustion behaviour of pre-dried Greek lignite

The present paper includes the results of the combustion tests with Greek dried lignite performed at a 1 MWth semi industrial scale pulverized coal combustion facility. Scope of the campaign is the investigation of the combustion behaviour of Greek lignite, i.e. temperature fields, ignition, burnout, emissions, as well as slagging and fouling tendency, while firing with varying levels of recirculated flue gas. Dry coal co-firing conditions in a large scale boiler are simulated by adjusting the volume flow of recirculated flue gas.Two test series representing different boiler operation modes are performed. During the first series the maximum flue gas temperature increase, when co-firing dry coal, is determined, while in the second test series the needed load decrease, in order to keep constant furnace outlet temperature in dry coal co-firing conditions is recorded. A detailed measurement set is carried out including temperature profiles, emissions, fuel, fly ash sampling and slagging and fouling investigations through the installation of dedicated deposition probes.The anticipated increase of the furnace temperature profiles by decreasing the inserted recirculated flue gas is confirmed by the experimental results. No clear trend of dry coal co-combustion on the emissions' behaviour is noticed, while dry coal firing appears to have a moderate effect on the deposition behaviour of Greek lignite. These preliminary investigations indicate that no significant operational problems are expected during a potential future demonstration of dry lignite co-firing in a Greek large scale boiler.     

Effect of Chemical Compositions on Ash Fusibility Characterization of a Jincheng Anthracite during Combustion and Gasification

The ash melting temperature of coal ash has an important effect during the fluidized bed combustion and gasification process, which affects the slagging and deposition characteristics of the boiler. Experiments on the effects of chemical components on the ash fusion behaviors have been completed on the ash fusion temperatures (AFTs) analyzer under typical gasification and combustion atmospheres. Meanwhile, calculations on the variation of minerals in ash with ash composition were conducted using the FactSage software. The results indicated that the AFTs under gasification were a little higher than those under the combustion atmosphere. On increasing the Fe₂O₃, CaO, and Na₂O contents under the combustion and gasification atmospheres, the four temperatures deformation temperature (DT), softening temperature (ST), hemispherical temperature (HT), and flow temperature (FT) decreased dramatically and the generation and transformation of minerals occurred. The iron-containing minerals, such as hercynite and fayalite, formed with increase in the content of Fe₂O₃; the Ca-bearing feldspar minerals, like gehlenite and anorthite, started appearing on increasing the CaO content, and the Na-containing feldspar minerals, like carnegieite, were detected as the Na₂O was increased. These three minerals can form low-temperature eutectics, decreasing the fusion temperature.     

煤催化气化工艺中内蒙王家塔烟煤灰烧结温度的影响因素分析

煤催化气化工艺中碱金属催化剂的引入加剧了气化炉的结渣,直接影响了流化床气化炉结渣的正常操作。煤灰的烧结特性是流化床气化炉结渣的主要影响因素之一,通过摸索工艺条件使煤气化在烧结温度以下运行,可有效避免流化床气化炉内出现结渣问题。利用压差法测定烧结温度,结合灰渣的XRD分析结果系统研究了钾基碱金属催化剂的添加量、操作压力、反应气氛对王家塔烟煤低温灰化煤灰烧结温度的影响。结果表明,碳酸钾催化剂的添加明显降低了煤的灰熔点及烧结温度。0.1～3.5 MPa下,烧结温度随压力增大而降低,而且压力对烧结温度的影响在高压区更为明显,具体影响规律与煤种灰成分及钾基碱金属催化剂的添加有关。空气、CO₂氧化性气氛下的烧结温度较高,N₂惰性气氛下次之,还原性气氛下较低,而蒸汽的加入显著降低了烧结温度。烧结温度的变化与不同气氛下铁离子存在状态及钾的存在形态密切相关。蒸汽气氛下,钾更多以KOH等低熔点化合物形态存在,而且含钾物相在蒸汽气氛下更容易同煤灰中的硅铝、铁钙等矿物质反应,生成低共融点化合物,致使灰熔点及烧结温度大幅下降。