煤催化气化催化剂发展现状及研究展望

煤与气化剂(如水蒸气、CO2、H2和O2)之间的气化反应最有效的催化剂主要为碱金属、碱土金属以及过渡金属的盐类,根据其组成,详细论述了煤催化气化催化剂的特性。据研究,在气化反应中碱金属催化剂如Na、K等易与煤中矿物质如Si或Al反应致使催化剂失活,同时过渡金属易被煤中S毒化,这在一定程度上制约了煤催化气化工业化进程。论述了煤催化气化催化剂的研究方向,认为开发新型高效、低廉且易回收催化剂是有必要的。     

煤催化加氢气化研究进展

煤加氢气化制天然气技术具有工艺路径短、热效率高等优点,其应用基础研究备受关注。但煤中存在部分致密的芳香碳结构,加氢反应性较差,即使在苛刻的反应条件下(~1 000℃、~7 MPa H_2),仍难以转化。通过引入催化剂,进行煤催化加氢气化可在温和的反应条件下实现煤的碳转化率和CH_4收率的同步提高。论述了碱金属(K、Na等)、碱土金属(Ca)和过渡金属(Fe、Co、Ni等)催化剂对模型碳加氢气化的催化作用原理。探讨了反应温度、氢气压力、和碳结构对C-H_2催化反应的影响规律,分析了适用于原煤催化加氢气化的最佳催化剂及工艺条件,并从CH_4和轻质液体焦油等产物生成规律、煤中碳结构随着反应进行的衍变过程等角度,讨论了催化剂分别对煤加氢热解和热解半焦加氢气化的催化作用行为。提出了煤催化加氢气化联产CH_4和轻质液体焦油技术从基础走向应用的进一步研究建议。现有研究结果表明,过渡金属与碱土金属组成的二元催化剂(Fe/Co/Ni-Ca)对煤加氢气化的活性较高。过渡金属元素在反应过程中主要提供C-H_2反应所需的活性氢,并削弱C—C键的键能;碱土金属元素Ca主要促进Fe/Co/Ni的分散,防止其发生硫中毒失活,并增强Fe/Co/Ni与碳之间的相互作用。温度升高一方面为化学键断裂过程提供了更高能量,加速C-H_2反应,另一方面促进催化剂在煤结构中扩散,提升催化剂的供氢和断键效率。升高压力促进了活性氢的供应,同时CH_4浓度得到稀释,反应向生成CH_4的方向移动。以5%Co-1%Ca为催化剂,在850℃、3 MPa H_2反应条件下,30 min内可同时达到90.0%的碳转化率和77.3%的CH_4收率。Co-Ca催化剂在煤加氢热解过程中具有催化解聚和催化加氢的作用,提高焦油和CH_4收率,同时催化剂在煤加氢热解过程中对煤结构产生催化活化作用,使得生成的半焦具有较高的气化活性。煤催化加氢气化的机理研究目前仍处于推测阶段,另外,该技术气化剂、煤种的适应性,催化剂循环利用性能有待进一步阐明。     

生物质/煤共气化协同作用的产生及强化机制

生物质中碱金属的催化作用是引起共气化协同作用的根本原因。然而,共气化过程中碱金属易与煤中矿物质反应生成硅铝酸盐等没有催化活性的物质,导致不能发挥出有效的催化作用。因此为了部分抑制共气化过程中生物质碱金属的失活,强化协同作用,通过固定床热解、共热解焦水蒸气气化实验,考察了小麦秸秆和晋城无烟煤共气化过程的反应性和协同作用,并通过添加钙基添加剂的方式,强化了协同作用,提高了共气化反应速率。研究发现共热解焦在气化过程中虽然表现出协同作用,但仍然存在K的失活。考察了钙基添加剂的种类、添加量、添加顺序等对共气化反应的影响,结果表明：钙基添加剂使共热解焦比表面积增大,碳结构无序化程度增强,活性位点增多,并通过与煤中SiO₂等矿物质的结合,部分阻止了K的失活,使共热解焦中水溶性K含量升高,反应速率提高。Ca(Ac)₂表现出最优的共气化反应促进作用,其最优添加量为7.5%。气化反应动力学的研究表明,Ca(Ac)₂的添加降低了共热解焦的气化反应活化能。修正随机孔模型(S-MRPM)适合描述小麦秸秆焦、晋城煤焦和共热解焦的气化反应特性,随机孔...     

新疆准东高碱煤流态化气化过程中碱金属的迁移特性

在0.25 t/d高碱煤热化学转化热态实验台上对不同气化温度下神华准东高碱煤中碱金属的迁移分配特性进行了实验研究.结果表明,煤中Na主要以水溶态形式存在,K主要以不溶态形式存在.在不同气化温度下,底渣中的Na含量总体上高于循环灰中,气化温度越高对飞灰中Na,K的迁移分配特性影响越显著,Na,K迁移特性差异明显.在850?1 000℃气化条件下,煤中86.7%?93.1%的Na冷凝富集于飞灰中,主要以Na Cl晶相形态存在.     

催化气化过程中Na催化剂失活与Na-Al复合转化行为

催化气化是一种新型煤气化方式，催化气化催化剂主要为碱金属催化剂，但在催化气化过程中碱金属催化剂会与煤中Si、Al矿物质相互反应，直接影响碱金属催化气化催化活性。以Na₂CO₃为催化剂，分析催化气化过程中碱金属失活行为与Na-Al复合转化行为，采用高岭石和勃姆石为模型化合物对Na-Al复合与转化过程进行研究，并对比Na-Al转化产物的催化作用。研究表明：Na₂CO₃催化作用良好，催化气化过程中Na₂CO₃与煤中Si、Al矿物质反应，生成霞石与硅铝酸钠类物质，导致催化剂失活。高岭石与Na₂CO₃在700℃开始反应，生成硅铝酸钠类物质。勃姆石与Na₂CO₃在860℃时反应生成偏铝酸钠，偏铝酸钠高温下不稳定，进一步转化为硅铝酸钠类物质。与Na₂CO₃相比，硅铝酸钠与偏铝酸钠的催化效果较差，导致碱金属催化作用下降，同时，生成的偏铝酸钠催...     

碱金属及灰分对煤焦碳微晶结构及气化反应特性的影响

通过对原煤、酸洗原煤、酸洗后负载NaOH的原煤在750~1050℃热解制得焦样,用X射线衍射技术考察了热解温度、NaOH负载量以及灰分对热解过程中煤焦微晶结构变化的影响,并运用高温高压热天平(PTGA)考察了热解后煤焦的气化反应活性。结果表明碱金属及灰分的存在可以明显减小煤焦的微晶结构参数的变化(堆垛高度Lc、微晶尺寸La、及晶层间距d002),阻碍煤焦的石墨化进程,提高煤焦的气化反应性。随着热解温度的升高,堆垛高度Lc增大显著,而微晶尺寸La和晶层间距d002变化较小。煤焦的气化反应性k0和煤焦微晶结构参数Lc、d002存在如下关系:lnk0=a(Lc/d002)+b;研究还表明用氧化还原循环机理来描述碱金属的催化作用机理是不恰当的,但碱金属Na的存在可以明显降低煤焦的石墨化程度,提高煤的活性,对煤焦的气化起到部分催化作用。     

准东煤水热提质及废液催化气化特性研究

准东煤的碱金属(特别是Na、Ca)含量高,直接作为动力煤燃烧会导致严重的锅炉沾污、结渣。采用水热提质方法能够有效脱除煤中碱金属,同时还可改善煤质的理化特性,但水热提质也会产生大量废液,并导致有机质损失,原料的能量利用率低,限制了该方法的应用。针对上述问题,将水热提质技术与废液气化技术进行耦合,在水热反应釜和自制的两段式反应装置上开展了准东煤水热提质改性及衍生废液催化气化的试验研究,探究了提质后三相产物的分布特性及废液的催化气化特性。结果表明,随着水热温度的升高,煤样的固体回收率降低,废液中总有机碳(TOC)和气体产物显著增大,但至少有97.8%的碳元素分布在固相产物中。废液催化气化产生了富含CH_4、H_2的可燃气,最高占比达到70%。Ni/C催化剂中Ni元素对废液的气化起催化作用,催化效率随着水热温度、气化温度的升高而升高,随液时空速的升高而降低。优选的催化气化试验条件:Ni/C催化剂、水热温度为300℃、催化气化温度为350℃和液时空速为150 h-1。总之,水热提质-废液催化气化联用技术既可以实现煤质的改性,又回收了废液中的能量,能够为准东煤的清洁、高效利用提供新的思路。     

可弃性催化剂在GE水煤浆气化技术中的应用探讨

煤催化气化技术最主要的就是催化剂,然而对于一些传统的催化剂因为其价格高以及回收率低和对环境会造成一定的影响等,对于煤催化气化的工业发展有一定的影响,对于可弃催化剂来讲其主要作为一种能够加速煤气化的反应,并且较为廉价和有效,逐渐地引起了人们的重视。尤其是在当前社会可持续发展理念下,可弃催化剂作为一种加速煤气化反应的廉价且有效的催化剂被广泛应用。主要对GE水煤浆气化中石灰石和添加剂(造纸黑液)的催化性能进行探讨,介绍了可弃性催化剂在GE水煤浆气化技术中的应用。     

液化残渣气化过程钠/铁协同催化作用及对焦结构演化的影响规律

高钠煤直接液化后碱金属钠富集于液化残渣中，相比原煤，残渣的钠含量升高4～10倍，利用残渣固有钠及残留的铁基液化催化剂对液化残渣进行催化气化提质，是其资源化高效利用的理想方案。通过煤直接液化实验制取了钠含量较高的高碱液化残渣，研究了高碱液化残渣在气化过程中钠/铁协同催化的反应性，并建立适宜的动力学模型，考察了协同催化反应的动力学过程。围绕钠/铁间高温相互作用规律，通过联合FTIR,XRD,ICP-AES等技术，详细分析了气化焦有机结构、矿物质组成及钠高温释放率等。结果表明：钠/铁协同催化过程的活化能为66 kJ/mol～69 kJ/mol,与高碱液化残渣单独气化相比均有所降低，残渣最高气化反应性指数超过0.45°/min,相同温度下液化残渣最大反应速率分别增大了1.17倍(900℃)、1.33倍(1 000℃)和1.14倍(1 100℃);双金属间表现出明显的协同催化效应，n(Na)/n(Fe)对液化残渣气化反应性有一定影响，铁含量较高时易形成弱催化活性的铁/碱金属化合物K-Fe, Na-Fe和Li-Fe等，从而降低协同催化活性，且气化温度升高有利于强化铁与碱金属间结合作用；XRD分析同...     

煤与生物质共气化制甲烷实验研究

以烟煤和高粱秸秆为研究对象,在小型加压固定床反应器上考察了压力3.5MPa及温度700℃条件下制焦方式、煤/生物质混合比和气固接触时间对煤与生物质共气化制取富甲烷气体过程中水蒸气气化反应和甲烷化反应的影响.结果表明,对于水蒸气气化反应,煤焦和生物质焦共气化时不能观察到明显的协同作用;对于甲烷化反应,高粱秸秆焦的甲烷化反应活性高于煤焦的甲烷化反应活性,当对高粱秸秆水洗后,高粱秸秆焦的甲烷化反应活性降低至与煤焦的甲烷化反应活性相当,分析表明,水洗后高粱秸秆焦碱金属钾的含量显著降低,说明高粱秸秆焦中碱金属钾的存在是高粱秸秆焦甲烷化反应活性较高的主要原因.增加气固接触时间,有利于提高甲烷产率.     

碱金属对煤热解和气化反应速率的影响

通过对原煤、酸洗原煤、负载碱金属的酸洗原煤在800～1050℃热解制得焦样,用X射线衍射技术考察了碱金属对煤焦微晶结构的影响,在加压热天平（PTGA）上考察了煤样的热解过程,以及焦样的二氧化碳气化活性。结果表明：碱金属对煤的热解和气化阶段都有影响。在热解阶段,碱金属的存在抑制了煤焦的石墨化进程,降低了热解反应活化能,促进了热解反应的进行;在气化阶段,作为催化剂的碱金属,降低了气化反应活化能,延长了反应速率达到最大值的时间。修正的随机孔模型可以较好地描述煤焦-CO₂的气化反应过程。     

平顶山高灰熔融性温度煤的气化反应性研究

介绍了平顶山地区有代表性的7种煤样在800℃～1 200℃下,其脱灰煤焦-CO2气化反应活性的实验,主要考察了煤种、灰含量及粒径对煤焦反应性的影响,实验结果表明:煤种对煤焦-CO2气化反应有明显影响;煤中灰分对煤焦气化反应的影响主要表现在两个方面,一是灰成分对煤焦气化反应的催化作用,二是灰熔融性影响煤焦气化排渣行为。脱灰既可以除去煤焦中具有催化作用的矿物质,又可以增大煤焦的内表面积。     

Reactivities of 34 coals under steam gasification

The reactivities of 34 coal chars of varying rank with H₂O have been determined to examine the effect of coal rank on the gasification rate of coal char. The reactivities of chars derived from caking coals and anthracites (carbon content > 78 wt%, daf) were very small compared with those from non-caking (lower-rank) coals. The reactivities of low-rank chars do not correlate with the carbon content of the parent coals. To clarify which factor is more important in determining the reactivity, the evolution of CO and CO₂ from char, the moisture content of char and the amount of exchangeable cations were determined for these low-rank coals or their chars. These values were considered to represent the amount of active carbon sties, the porosity and the catalysis by inherent mineral matters, respectively. It was concluded that the amount of surface active sites and/or the amount of exchangeable Ca and Na control the reactivity of low-rank chars in H₂O.     

Catalytic gasification of char from co-pyrolysis of coal and biomass

The catalytic gasification of char from co-pyrolysis of coal and wheat straw was studied. Alkali metal salts, especially potassium salts, are considered as effective catalysts for carbon gasification by steam and CO₂, while too expensive for industry application. The herbaceous type of biomass, which has a high content of potassium, may be used as an inexpensive source of catalyst by co-processing with coal. The reactivity of chars from co-pyrolysis of coal and straw was experimentally examined. The chars were prepared in a spout-entrained reactor with different ratios of coal to straw. The gasification characteristics of chars were measured by thermogravimetric analysis (TGA). The co-pyrolysis chars revealed higher gasification reactivity than that of char from coal, especially at high level of carbon conversion. The influence of the alkali in the char and the pyrolysis temperature on the reactivity of co-pyrolysis char was investigated. The experimental results show that the co-pyrolysis char prepared at 750 °C have the highest alkali concentration and reactivity.     

Volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of Victorian brown coal. Part IV. Catalytic effects of NaCl and ion-exchangeable Na in coal on char reactivity

The purpose of this study is to investigate the catalytic effects of Na as NaCl or as sodium carboxylates (-COONa) in Victorian brown coal on the char reactivity. A Na-exchanged coal and a set of NaCl-loaded coal samples prepared from a Loy Yang brown coal were pyrolysed in a fluidised-bed/fixed-bed reactor and in a thermogravimetric analyser (TGA). The reactivities of the chars were measured in air at 400 °C using the TGA. The experimental data indicate that the Na in coal as NaCl and as sodium carboxylates (-COONa) had very different catalytic effects on the char reactivity. It is the chemical form and dispersion of Na in char, not in coal, that govern the catalytic effects of Na. For the Na-form (Na-exchanged) coal, the char reactivity increased with increasing pyrolysis temperature from 500 to 700 °C and then decreased with pyrolysis temperature from 700 to 900 °C. The increase in reactivity with pyrolysis temperature (500-700 °C) is mainly due to the changes in the relative distribution of Na in the char matrix and on the pore surface. For the NaCl-loaded coals, when Cl was released during pyrolysis or gasification, the Na originally present in coal as NaCl showed good catalytic effects for the char gasification. Otherwise, Cl would combine with Na in the char to form NaCl during gasification, preventing Na from becoming an active catalyst. Controlling the pyrolysis conditions to favour the release of Cl can be a promising way to transform NaCl in coal into an active catalyst for char gasification.     

复合碱型腐植酸型煤粘结剂的特性研究

研究了从云南褐煤提取型煤腐植酸粘结剂的过程,主要考察了煤碱质量比和不同碱性添加物包括NaOH,Na4P2O7,Na2CO3和K2CO3等对腐植酸提取率的影响,并进行了成本估算。结果表明,在利用NaOH的条件下,煤碱质量比在10∶1与12∶1之间获得较好提取效果;与利用单一NaOH添加剂相比,在总碱量略有减少的前提下,用Na4P2O7和Na2CO3替代部分NaOH使腐植酸的提取率增加18.4%,粘结剂的粘度提高30%,经济成本下降2.6%。腐植酸钾型型煤的气化效果好于钠型,跌落强度基本相同。     

Effects of alkaline metal on coal gasification at pyrolysis and gasification phases

A Chinese high-rank coal was acid-washed and ion-exchanged with Na and K to prepare the H-form, Na-form and K-form coals. After pyrolysis, H-form, Na-form and K-form chars and two additional H-form chars (acid washed Na-form and K-form chars) were prepared to investigate the effects of alkaline metal (AM) on coal gasification at the pyrolysis and gasification phases. The H-form char had the highest pryolysis rate; the H-form char had a relative low gasification rate. The AM loaded coals exhibited relative low pyrolysis rate, while the corresponding chars had high gasification reactivity. Acid-washing reduced the reactivities of Na-form and K-form chars. AM inhibited the progress of graphitization of the base carbon resulting in a more reactive char of less ordered crystalline carbon structure. A kinetic model incorporating AM-catalyzed gasification and non-catalytic gasification was developed to describe the gasification rate changes in the char conversion for AM-catalyzed gasification of chars.     

Catalysis of gasification of coal-derived cokes and chars

Calcium is the most important in-situ catalyst for gasification of US coal chars in O₂, CO₂ and H₂O. It is a poor catalyst for gasification of chars by H₂. Potassium and sodium added to low-rank coals by ion exchange and high-rank coals by impregnation are excellent catalysts for char gasification in O₂, CO₂ and H₂O. Carbon monoxide inhibits catalysis of the CH₂O reaction by calcium, potassium and sodium; H₂ inhibits catalysis by calcium. Thus injection of synthesis gas into the gasifier will inhibit the CH₂O reaction. Iron is not an important catalyst for the gasification of chars in O₂, CO₂ and H₂O, because it is invariably in the oxidized state. Carbon monoxide disproportionates to deposit carbon from a dry synthesis gas mixture (3 vol H₂ + 1 vol CO) over potassium-, sodium- and iron-loaded lignite char and a raw bituminous coal char, high in pyrite, at 1123 K and 0.1 MPa pressure. The carbon is highly reactive, with the injection of 2.7 kPa H₂O to the synthesis gas resulting in net carbon gasification. The effect of traces of sulphur in the gas stream on catalysis of gasification or carbon-forming reactions by calcium, potassium, or sodium is not well understood at present. Traces of sulphur do, however, inhibit catalysis by iron.     

TPR法研究煤焦—CO_2气化反应──（Ⅰ）碳化条件和掺加金属催化剂对气化反应性的影响

改变碳化条件和掺加金属催化剂，制备了十几个煤焦样品。用ＸＲＤ测定了未载金属煤焦的碳微晶尺寸。用ＴＰＲ法测定了上述煤焦的ＣＯ_２气化反应性，用Ｆｒｅｅｍａｎ－Ｃａｒｒｏｌｌ方法计算得到了反应活化能Ｅ和指前因子Ａ。结果表明：碳化条件越剧烈，煤焦的气化活性越低。掺加不同量的钙催化剂，煤焦的气化活性得到不同程度的提高，同时ＤＴＧ曲线有明显的变化。这些现象可从碳化条件对煤焦气化活性的影响，以及钙对煤焦ＣＯ_２气化的催化作用等方面来解释。