煤中固有矿物质在热解过程中对氮释放的影响

采用管式炉固定床反应器,考察了平朔煤( PS)、神木煤( SM)和阳城煤( YC)三种不同变质程度的煤种在热解过程中的HCN和NH3 释放规律,主要讨论煤中所固有的矿物质在这一过程中对氮分配的影响.结果表明:不同变质程度的煤种脱除矿物质后,均表现为热解过程中的NH3释放量减少,其减少程度与灰分的性质有关;而HCN的释放与煤中矿物质的关系却受煤变质程度的影响;同时矿物质对不同形态氮的分配也有明显的作用.     

矿物质对煤中硫氮在热解气化过程中迁移变化的催化作用

从煤自身所含的矿物质和外加添加剂的观点出发,对煤热解、气化和燃烧过程中存在的催化作用进行了阐述,尤其是煤中N、S有害元素的催化转化作用。煤自身所含的矿物质及部分碱金属、碱土金属和过渡金属添加剂对煤热解、气化和燃烧过程具有一定的催化能力,同时对煤中N、S有害元素的转化也有明显作用。对具有单功能催化作用的金属催化剂进行合理组合、适当改性和优化添加方式,在NOx和SOx污染性气体形成前对其前驱体进行抑制和定向转化,是今后煤炭洁净转化的一个研究方向。     

煤中矿物质与气化工艺的选择

考察了煤中矿物质对气化工艺选择的影响关系,介绍了国内外有关的研究进展。研究表明,煤灰的熔融特性及粘－温特性是气化工艺排渣方式选择的决定因素。煤的灰熔点及灰粘度不但与煤灰的化学组成有关,而且与煤灰的矿物形态有关,且与相平衡性质有较好的相关性。这为研究控制煤灰熔点、扩大气化工艺选择提供了较好的理论基础。     

煤热解过程中氮元素迁移规律影响因素

由于散煤燃烧会造成严重的环境污染,尤其是其排放的氮氧化物对大气环境破坏严重,煤热解作为煤燃烧、气化的伴随过程,具有重要的研究意义,而探究煤中氮元素在热解过程中的迁移规律,了解氮氧化物前驱物的生成条件对后续含氮污染物的控制起到决定性作用,在实际的热解过程中,多种因素共同制约着含氮物相的迁移方向,通过煤阶、粒径、热解温度、矿物质种类这些影响因素,可以得到:煤阶越高,挥发分越不易析出,在一定程度上,高煤化度煤氮易留在焦中,中等煤化度煤氮则易于进入挥发分中,煤颗粒粒径越大,挥发分也同样不易析出,而热解温度则对挥发氮和焦氮形成均有促进作用,不同金属离子对含氮物相析出有不同的效果。     

固体热载体煤热解过程中氮的迁移

在固体热载体煤热解实验装置上考察了石英砂、燃烧灰和气化半焦为热载体对煤热解过程中氮迁移的影响.固体热载体煤热解过程中,热解温度升高有利于煤中挥发分析出,可以促进煤中含氮官能团发生断键,利于氮的脱除.快速热解可促进煤中氮脱除生成HCN和NH3.分别以石英砂、燃烧灰和气化半焦为热载体,研究表明:热载体中矿物质可促进焦油氮分...     

铁镍复合助剂对煤热解过程中氮迁移规律的影响

为了减少煤炭燃烧过程中NO_x的排放,在管式炉中进行了煤与金属助剂（FeCl₃、NiCl₂）的热解实验,研究了助剂负载量、热解温度、助剂添加方式对氮迁移及N₂产率的影响并且对复合助剂作用机理进行了探讨。结果表明：随着助剂负载量的增加,氮脱除率及N₂产率呈现先增加后趋于稳定的趋势,且负载量以0.8%Fe复合1.0%Ni为最佳。在700~1000℃的热解温度范围内氮脱除率及N₂产率随热解温度的增加而增加。对煤进行溶胀处理添加复合助剂后,氮脱除率及N₂产率要优于未经处理的煤样。铁基助剂与镍基助剂在催化煤热解氮迁移过程中形成互补,铁基助剂的添加增加了镍基助剂的活性,弥补了单助剂的劣势,且复合助剂相比于单助剂有更强的氮脱除效果并且N₂产率达到最高39%。铁镍复合助剂对煤中N-5转化为N₂的催化效果更加明显,因为复合助剂对吡咯的内氢转移和开环有更强的催化作用。本研究能够为煤炭洁净化利用提供理论和实验依据。     

煤热解过程中S、N与矿物质作用情况综述

简要介绍了矿物成分、S和N在煤中的赋存形态,详述了煤热解时S、N析出的形态以及矿物质和S、N相互作用的研究进展,并指出应加强煤热解过程中S、N和矿物质作用机理的研究,以促进煤的清洁利用,减少环境污染。     

煤中矿物质对神府煤快速液化的影响

利用共振搅拌反应器研究了煤中矿物质对神府煤高温快速液化的影响。原料煤经酸洗去除煤中大部分矿物质,脱灰率可达84．83％。脱灰后的煤在490℃进行加氢液化,结果表明,煤中矿物质的降低对神府煤高温快速液化有较大的影响,尤其影响了煤的初始高活性,煤转化率及液化产物的产率都降低,且煤中矿物质的降低会使矿物质自催化作用减弱,影响了神府煤液化产物质量。     

不同变质煤热解和气化中燃料氮的转化规律

利用水平管式炉对不同变质程度煤进行了热解和气化实验,并利用傅里叶红外气体分析仪对热解和气化过程中主要含氮产物的释放规律进行了研究.结果发现,煤的变质程度对煤热解和气化过程中HCN的释放具有重要影响,而对NH3的释放影响较小.对于低变质程度煤来说,挥发分含量较高,而挥发分的深度裂解是HCN产生的主要来源.因此,低变质程度煤热解过程中转化为HCN的燃料氮份额高于高变质程度煤;对于不同变质程度煤在热解过程中转化为NH3的燃料氮份额则大致相当.对不同变质程度煤在CO2气氛条件下气化反应过程中含氮产物生成规律的研究发现,焦炭氮几乎全部转化为NO;转化为NH3的燃料氮份额有所增加;除印尼褐煤外,转化为HCN的燃料氮份额也有所增加;此外,对CO2气化过程中NO的生成机理进行分析,认为焦炭氮的直接氧化可能是NO产生的主要来源.     

Kinetics of mineral matter transformation during coal combustion

The transformation of individual minerals was investigated based on TG and DTG analysis at temperature up to 1700 K in inert and oxidizing atmospheres. The decomposition of minerals in inert atmosphere and the reaction with gaseous atmosphere was described by first order reactions for which the kinetic data were found. The evaluated kinetic parameters were then tested on a complex mineral matter of coals. It has been demonstrated on example of two different compositions that the mass loss during the transformation of coal mineral matter during combustion can be modelled as a mixture of individual minerals.     

Effect of mineral matter on coal self-heating rate

Adiabatic self-heating tests have been conducted on subbituminous coal cores from the same seam profile, which cover a mineral matter content range of 11.2-71.1%. In all cases the heat release rate does not conform to an Arrhenius kinetic model, but can best be described by a third order polynomial. Assessment of the theoretical heat sink effect of the mineral matter in each of the tests reveals that the coal is less reactive than predicted using a simple energy conservation equation. There is an additional effect of the mineral matter in these cases that cannot be explained by heat sink alone. The disseminated mineral matter in the coal is therefore inhibiting the oxidation reaction due to physicochemical effects.     

Reaction of catalysts with mineral matter during coal gasification

After a review of mineral matter of German hard coal, its reactions with catalysts during gasification with steam to form new crystalline phases are dealt with. Products of commercial plants and laboratory experiments were investigated by means of microscopy, XRD, XRF and microprobe analysis.     

A review on nitrogen transformation and conversion during coal pyrolysis and combustion based on quantum chemical calculation and experimental study

The emission of NOx during coal combustion contributes to the formation of acid rain and photochemical smog,which would seriously affect the quality of atmospheric environment.Therefore,the decrease of NOx is of great importance for improving the efficient utilization of coal.The present review comprehen-sively summarized the influence factors and mechanisms of migration and transformation of nitrogen during the coal pyrolysis and combustion based on experimental study and quantum chemical calcula-tion.Firstly,in the process of pyrolysis:the occurrence state and transformation of nitrogen were con-cluded.The influence of temperature,atmosphere,heating rate and catalyst on formation of NOx precursor and nitrogen migration path at the molecular level were summarized;Secondly,during the process of combustion:the influence of temperature,ambient oxygen concentration,physical structure of coal char,catalyst on heterogeneous oxidation of char (N) were summarized;The effects of char sur-face properties,catalyst and ambient atmosphere on heterogeneous reduction of NOx were also con-cluded.Based on the quantum chemical calculation,the reaction path of heterogeneous oxidation of char-N and heterogeneous reduction of NOx were described in detail.Current studies focus more on the generation of HCN and NH3,but in order to reduce the pollution of NOx from the source,it is necessary to further improve the process conditions and the optimal formula of producing more N2 during pyrol-ysis,as well as clarify the path of the generation of N2.Experiments study and quantum chemistry cal-culation should be combined to complete the research of directional nitrogen reduction during pyrolysis and denitration during combustion.     

高氯准东煤中典型矿物元素对颗粒物生成的影响

在高温沉降炉上,进行了高氯高碱准东煤、低氯低碱准东煤和由低氯准东煤处理制得的调质准东煤在含不同浓度HCl的模拟空气中的燃烧实验。利用DLPI进行了颗粒物的分级收集,对其质量粒径分布和矿物元素分布特性进行了讨论分析。结果表明,高氯高碱准东煤的超细模态颗粒物生成量和峰值粒径均明显大于其他两种煤,其主要成分为Na和Cl。Ca的迁移特性与其形态密切相关,原煤中的Ca主要以无机矿物形式存在,主要迁移进入粗颗粒物而对超细颗粒物生成贡献较小。气氛中加入不同浓度HCl气体后,低钠煤和调质煤产生细颗粒物中Cl含量均升高,但生成量无显著变化。表明HCl并未显著促进矿物的气化,但会促进NaCl形式矿物蒸气的形成,进而促进成核形成超细颗粒物。     

脱矿物质过程对煤结构影响的研究

选取神华煤和兖州煤两种煤样,用盐酸和氢氟酸处理脱去其中的矿物质,并且脱矿物质前后的煤样在氧化性气氛下,制成815℃的煤灰。利用红外光谱研究其矿物质组成以及处理前后煤结构的变化。结果表明：酸处理法能够脱除煤中大多数矿物质。2种煤灰中,矿物质组成主要是石英、硬石膏、方解石、高岭土和含铁矿物质,但含量不同。处理前后,煤结构中的含氧官能团发生了一定的变化。     

添加木质素对污泥热解过程氮转化的影响

利用热重-质谱联用仪（TG-MS（在线检测添加不同比例木质素的污泥热解和主要含氮气体释放特性,并利用傅里叶红外光谱仪（FTIR（在线检测热解过程固体残焦表面官能团的变化规律,分析木质素对污泥热解过程氮转化的影响,从而揭示氮的迁移机理。结果表明：污泥热解过程NH₃的生成主要来自蛋白质的脱氨作用,加入木质素后热解过程中产生了大量羰基,抑制了氨基酸的分子内环化和分子间缩聚反应,而促进了直链酰胺的生成,最终在OH自由基攻击下转化成HNCO和HCN;NH₃的增加并非来自HCN和OH的反应,而是由未缩合的氨基脱除生成;另外,添加40%左右的木质素对于减少污泥热解过程中NO_x前驱物的排放有积极意义。     

Influence of mineral matter in coal on decomposition of NO over coal chars and emission of NO during char combustion

NO-char reaction and char combustion in the presence and absence of mineral matter were studied in a quartz fixed bed reactor. Eight chars were prepared in a fluidized bed at 950 °C from four Chinese coals that were directly carbonized without pretreatment or were first deashed before carbonization. The decomposition of NO over these coal-derived chars was studied in Ar, CO/Ar and O₂/Ar atmospheres, respectively. The results show that NO is more easily reduced on chars from the raw coals than on their corresponding deashed coal chars. Mineral matter affects the enhancement both of CO and O₂ on the reduction of NO over coal chars. Alkali metal Na in mineral matter remarkably catalyzes NO-char reaction, while Fe promotes NO reduction with CO significantly. The effect of mineral matter on the emission of NO during char combustion was also investigated. The results show that the mineral constituents with catalytic activities for NO-char reaction result in the decrease of NO emission, whereas mineral constituents without catalytic activities lead to the increase of NO emission. Correlation between the effects of mineral matter on NO-char reaction and NO emission during char combustion was also discussed.     

Characterization and catalytic activity of coal mineral matter: 1. Effect of hydrogen pretreatment and exposure to sulphur and nitrogen compounds

Low temperature ash (LTA) samples prepared from nine US coals were characterized by X-ray diffraction. X-ray fluorescence, and surface area analyses. The results showed that illite, kaolinite, quartz and pyrite are major components in LTAs and that $\text{S}\text{Fe}$ ratios of some LTAs decreased significantly after H₂ treatment implying the occurrence of a partial reduction of pyrite during this treatment. Surface areas of LTAs increased drastically on H₂ treatment but decreased after exposure to sulphur and nitrogen compounds in activity testing. Correlations for the surface areas of LTAs before and after H₂ treatment were found in terms of clay content and element concentrations.     

Dialytic removal of particulate matter from coal conversion products

A dialytic procedure which is effective for the removal of microparticulate and colloidal-sized suspended matter from coal-derived liquids is described. The method involves passing the sample, dissolved in methylene chloride, through a latex rubber membrane. The dialytic procedure appears promising as a convenient method for production of large, particulate-free samples of coal conversion products. Application of the technique is illustrated by separation of a high particulate (≈30wt% insoluble materials) stripper bottom sample from the SRC-II process and subsequent analysis of the organic composition and metals content of the dialysate. The material which traverses the membrane, the dialysate, is shown to be a representative sample of the soluble organic portion of the material being dialysed and found to be essentially free of metals. The true solubility of the dialysate renders it easier to characterize via instrumental methods than the original sample containing large amounts of insoluble materials.