Volatile products from lignite pyrolysis and hydropyrolysis

Samples of three Louisiana lignites were subjected to atmospheric pressure pyrolysis and hydropyrolysis over a temperature range of 400–800 °C. Volatile products were collected in cold traps containing dichloromethane solvent and immersed in a salted ice bath. Volatiles were analysed using coupled gas chromatography/mass spectrometry and approximately 150 separate compounds were noted. Because the product complexity made definite identification of each compound impossible, all components were assigned to one of eleven compound groups and subsequent analysis of results was based upon these groups. The effect of atmosphere, nitrogen versus hydrogen, was found to have a significant impact on volatile composition. Increased concentrations of alkyl benzenes and other single ring compounds were found in the hydrogen product with corresponding reductions in alkanes and alkenes. Only trace concentrations of polyaromatic compounds containing more than two rings were found in either atmosphere. Volatile product composition differences between the three lignites were small. Similarly, the effect of temperature on composition was relatively unimportant.     

The influence of fast pyrolysis condition on biocrude-oil yield and homogeneity

The characteristics of biocrude-oil yield and quality have been investigated by changing fast pyrolysis condition for woody biomass. For the fast pyrolysis of woody biomass, a bubbling fluidized bed reactor having cylindrical shape was devised and a commonly used spiral quenching system was applied to the condensation of volatile gases from the reactor. Biomass feeding rate, nitrogen flow rate, pyrolysis temperature and particle size of woody biomass were changed to study the characteristics of volatile generation, its condensation and the homogeneity of the condensed biocrude-oil. In particular, the microscopic visualization of the collected biocrude-oil and its evaluation method by image processing technique were made for quantifying the homogeneity of the oil. From the results, the effects of heating and fluidization condition on the biocrude-oil yield and the homogeneity were fully scrutinized in a bubbling fluidized bed reactor. Also, the physical and chemical characteristics of the collected biocrude-oil were determined through various analysis techniques.     

Fixed-bed pyrolysis of coal under hydrogen pressure at low heating rates

Fixed-bed hydropyrolysis has been investigated by treating 100 g coal up to 900°C and 10 MPa. The devolatilization rate of Beringen coal (32.8 wt% volatile matter) treated on a fixed bed approximates to that obtained by flash hydropyrolysis. However, the oil yield is smaller because of the slower heating of the coal and the rather longer residence time of the primary volatile matter in the reaction space. The product gas is mainly methane. The oil composition depends on the temperature of pyrolysis. The benzene content of the oil rises with temperature. At constant temperature, the influence of hydrogen partial pressure is important between 0–1 MPa. At higher pressure, the yields and compositions vary only slightly with pressure. It has also been shown that from 580°C pyrolysis under hydrogen yields an additional quantity of water, when compared with pyrolysis under inert atmospheres or under atmospheric pressure. This additional water comes from the hydrogenation reactions of the hydroxyl functions of heavy phenols and xylenols. This implies a hydrogen consumption (from 0.2–0.3 wt% of the coal), varying with the pyrolysis temperature.     

非等温热重分析长焰煤热解过程与动力学特征

为提高煤热解过程中焦油的产率,用非等温热重分析方法研究了不同粒径、热解终温和升温速率条件下长焰煤的热解过程和机理,分析了20和100℃/min升温速率下长焰煤热解过程特征,并求解了热解动力学参数。结果表明,煤颗粒在2.8mm以下时,粒径对热解过程影响较小;热解终温越高,热解最终固体产物中挥发分产率越低;升温速率越快,挥发分的析出速率越快。在同一升温速率下,不同热解温度段得到的活化能呈现两头大中间小的特征,且指前因子随活化能的增大而增大。     

神木煤热解的挥发分收率与岩相组成的关系

引　言从构成煤的微观层次的显微组分入手研究煤的组成、结构和性质已成为煤化学研究的一个重要方面 ,在这方面一些研究者已做过许多有意义的尝试 ,主要集中在有关配煤制优质焦炭等方面[1] ,对于煤的热解挥发分收率与岩相组成相关联的研究也有零星报道 .Ｄｕｘｂｕｒｙ[2 ] 对一系列煤及其显微组分的热解研究结果表明 :不同煤的镜质组和惰质组的热解挥发分产率相差不大 ,相同量的不同煤种挥发分量的不同是由壳质组引起的 .其他研究者因不能得到纯度较高的显微组分而仅对热解过程中镜质组和惰质组的相互影响做过推测 .对于煤的挥发分收率与岩…     

Rapid devolatilization and hydrogasification of bituminous coal

Rapid devolatilization and hydrogasification of a Pittsburgh Seam bituminous coal were studied and an appropriate coal conversion (weight loss) model was developed that accounts for thermal decomposition of the coal, secondary char-forming reactions of volatiles, and homogeneous and heterogeneous reactions involving hydrogen. Approximately monolayer samples of coal particles supported on wire mesh heating elements were electrically heated in hydrogen, helium, and mixtures thereof. Coal weight loss (volatiles yield) was measured as a function of residence time (0–20 s), heating rate (65–10000 °C/s), final temperature (400–1100 °C), total pressure (0.0001–7 MPa), hydrogen partial pressure (0–7 MPa), and particle size (70–1000 μm). Volatiles yield under these conditions increases significantly with decreasing pressure, decreasing particle size, increasing hydrogen partial pressure and increasing final temperature, but only slightly with increasing heating rate. The data support the view that coal conversion under these conditions involves numerous parallel thermal decomposition reactions forming primary volatiles and initiating a sequence of secondary reactions leading to char. Intermediates in this char-forming sequence can escape as tar if residence time in the presence of hot coal surfaces is sufficiently short (e.g. low pressures and small particles well dispersed). Hydrogen at sufficiently high partial pressure can interrupt the char-forming sequence thereby increasing volatile yield. Rate of total product generation is largely controlled by coal pyrolysis while competition between mass transfer, secondary reactions, and rapid hydrogenation affects only the relative proportions of volatile and solid products formed.     

神木煤显微组分热解特性和热解动力学

在高压热天平上考察了神木煤显微组分在不同热解温度、压力和升温速率下的热解行为 .并利用分布活化能模型 (DAEM)研究了显微组分的热解动力学 .结果表明 :在相同的热解条件下 ,镜质组比丝质组有较高的挥发分收率 .随热解温度升高 ,镜质组和丝质组的挥发分收率增加 .热解升温速率和压力对镜质组和丝质组的挥发分收率略有影响 .DAEM的动力学处理表明 :镜质组的归一化热解速率高于丝质组 ,热解活化能较低.     

Nitrogen evolution during rapid hydropyrolysis of coal

The behavior of nitrogen evolution during rapid hydropyrolysis of coal has been investigated at temperatures ranging from 923 to 1123 K and hydrogen pressure up to 5 MPa using a continuous free fall pyrolyzer. Three coals have been tested in this study. The dominant nitrogen gaseous species is ammonia, together with a little amount of HCN because most of HCN is converted to NH₃ through secondary reactions. The results show that the evolution of nitrogen in coal is caused mainly by devolatilization at temperatures below 973 K, while the evolution of volatile nitrogen in char is accelerated with increasing temperature and hydrogen pressure. The mineral matter in coal act as catalysts to promote the evolution of volatile nitrogen in char to N₂ apparently at high temperatures of 1123 K, as found during pyrolysis of coal by Ohtsuka et al. A pseudo-first-order kinetic model was applied to the evolution of nitrogen in coal during rapid hydropyrolysis. The model shows the activation energy for the nitrogen evolution from coal is 36.6–58.6 kJ/mol while the rate of the nitrogen evolution depends on hydrogen pressure in the order of 0.16–0.24.     

Feasibility of the preparation of effective cheap adsorbents from lignites in rotary kiln

The feasibility to obtain effective cheap adsorbents using rotary kiln technology is studied for three lignites with different composition. The paper analyzes three different aspects, (i) relation between lignite origin and adsorption capacities of 4 nitrophenol, (ii) effect of the mineral matter content (amount and nature of ashes), (iii) pore volume distribution and surface area development. The lignite characteristics (i.e. water and volatile matter content) influence the pyrolysis behavior and the characteristics of the obtained chars and in consequence, the adsorption capacities. Optimal pyrolysis temperature has been determined for each precursor using a very simple and fast method in laboratory scale. We found temperature between 700 and 850°C. Moreover, we propose a simple thermal post-oxidation treatment which allows to strongly enhance the adsorption capacities. In our case, the higher volatile matter content, the higher ability to be oxidized leading to an improvement of the adsorption properties. The amount and nature of ashes seems to be a key parameter which positively influences the development of micro and mesoporosities. Moreover we have observed that a high degree of dispersion of mineral matter, and mostly calcium, allows to enhance reactivity of chars. Adsorption of 4 nitrophenol has been performed in batch reactor for all samples. Freundlich and Langmuir equations have been applied to the results. Very high adsorption capacities can be reached with some chars. For all samples which have different lignites precursor, we observed that adsorption capacities are twice more important after post-oxidative treatment. The feasibility of the preparation in rotary kiln of effective cheap adsorbents, starting from lignites has been demonstrated. Semi-pilot scale production of adsorbent having comparable adsorption properties in aqueous phase with commercial product has been realized.     

椰衣微波热解工艺的响应面法优化及液体产物组成分析

利用Box-Behnken试验设计，采用响应面法对椰衣微波热解工艺进行优化，考察了热解温度、氮气流速、升温速率和热解时间对液体产物产率的影响。试验结果表明：回归方程模型拟合较好且显著。各个因素对液体产物的产率影响的主次顺序为热解温度>氮气流速>热解时间>升温速率。最佳热解条件为热解温度550℃、氮气流速80 mL/min、升温速率20℃/min、热解时间25 min，在此条件下液体产物产率为38.28%。对液体产物的性质和组成分析发现：优化条件下得到的液体产物中含水量为14.32%，pH值为3.78，热值为24.61 MJ/kg。通过GC-MS对液体产物进行分析，最佳条件下得到的液体产物中主要含有酚、醛、酸、酮类化合物，分别为84.35%、6.01%、3.37%、2.05%，其中酚类化合物的量最高，包括苯酚（33.51%）、对甲酚（9.71%）、2-甲氧基苯酚（10.99%）和4-乙基-2-甲氧基苯酚（5.57%）。     

煤热解动力学模型的建立

通过对煤热解反应动力学分析,基于分布活化能模型DAEM,建立了集总反应动力学模型表示煤炭热解过程。确定了可以预测热解产物组成、分布与热解终温和升温速率关系的动力学方程。结果表明：随热解温度升高,各种挥发分产物析出率越来越接近最大产率;半焦C含量增加,但产率下降,H,O,N和S等元素降低。升温有利于提高半焦脱硫率、脱氮率。温度为600℃左右时,除H2外的大部分挥发分基本析出,半焦元素变化幅度减小。热解终温较低且一定时,较慢的升温速率有利于各热解挥发分最大限度析出。秦丽娜     

Flash pyrolysis of coals: influence of cations on the devolatilization behaviour of brown coals

The influence of cations on the pyrolysis behaviour of brown coals under flash heating conditions was investigated by means of a small fluidized-bed pyrolyser. A stream of coal particles in nitrogen was injected at rates of 1–3 g coal/h directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbons and total volatile matter from four Gelliondale brown coals and a Montana lignite were determined as a function of pyrolysis temperature. With all coals the maximum tar yield was obtained at 600 °C. Removal of cations present in the coals markedly increased the yields of tar and total volatile matter, with little effect on the yields of hydrocarbon gases. The converse was also observed in that the addition of Ca²⁺ to a cation-free coal decreased the yields of tar and total volatile matter. The extent of the reduction in tar yield at 600 °C in the presence of cations was found to be similar for all coals. After acid washing, tar yields appear to correlate with the atomic $\text{H}\text{C}$ ratios of the coals in a manner similar to that observed previously with bituminous coals.     

高粱秸秆热解产物的研究

研究了热解温度、气体流量、加热速率和保温时间三个操作因素对高粱秸秆热解产物(生物油和残炭)分布的影响。结果表明,对高粱秸秆热解产物的分布有很大影响的因素是热解温度和气体流速。在热解升温速率为10℃/min、热解温度为450℃,氮气流速为100mL/min、保温时间为1h的条件下,液体收率最高。     

几种年轻煤在氮热等离子体中的热解

研究了几种中国年轻煤在氮电弧热等离子体中的热解行为,考察了煤的基本性质、煤的粒度及加煤速率等条件对煤热解特性的影响.结果发现,煤在氮等离子体条件下热解所得气体产物中的主要成分是氢、乙炔、一氧化碳和丙炔腈,此外还有甲烷和乙烯等小分子烃.乙炔的收率随煤种的不同和操作条件的变化而波动.煤中的挥发分含量愈高、加煤速率愈低,乙炔收率则愈高.其中扎赉诺尔褐煤的乙炔收率最高可达22.3%(以煤中碳为基准);原料煤在氮等离子体中热解后,除部分芳香C—C键得以保留外,煤有机结构中的外围官能团全部消失,同时在热解半焦中有新的氮基官能团(如—C(?)N)引入.     

TG-MS联用技术研究木薯渣热化学特性

采用热重分析法和热重质谱联用技术并结合FTIR光谱考察了木薯渣的热化学特性,同时研究了厌氧处理的木薯渣和未经厌氧处理的木薯渣的热失量和气态产物的析出行为,结果表明厌氧处理的木薯渣和未经厌氧处理的木薯渣热解都可以分为3个阶段:水析出阶段(25~200 ℃)、挥发分析出阶段(200~600 ℃)和无机物的分解阶段(600~1 000 ℃),但未经厌氧处理的木薯渣在热解主体阶段有机质释放量高。利用TG-MS联用技术考察了2种原料的热解特性,发现两种木薯渣热解主要析出的气体要是H₂、H₂O、CO、CH₄和CO₂等,且气体生成曲线趋势类似。同时研究不同升温速率和粒径对木薯渣热解过程和氢气产物析出行为的影响,表明升温速率增加,H₂的产率在高温区增加,粒径增大有利于氢气的生成。根据Coats-Redfern积分法计算结果,木薯渣热解主体阶段的可用一级动力学方程描述,升温速率对木薯渣热解的活化能影响不大。     

A literature survey and an experimental study of coal devolatilization at mild and severe conditions: influences of heating rate, temperature, and reactor type on products yield and composition

Coal devolatilization studies to maximize the yield of condensable products by operating at elevated temperatures and heating rates have been published. The objectives of this study were to investigate the influences of relatively mild operating conditions (e.g. relatively low temperature and pressure) on product quality, by comparing devolatilized products obtained at various temperatures and heating rates. Fixed bed, fluid bed, and entrained flow reactor units were used to obtain pyrolysis products. In addition, literature data on tar yields in various reactor units at a range of temperatures and residence times were surveyed and compared with experimental data. The liquids were characterized by a number of techniques, including field ionization mass spectroscopy (f.i.m.s.), sequential elution solvent chromatography (s.e.s.c.) and elemental analysis. The results demonstrate that the quality and yield of liquids obtained at a rapid heating rate are functions of peak pyrolysis temperature. It was shown that at a rapid heating rate, the yields of heavier polyfunctional groups (i.e. hydrocarbons with greater mean molecular weight) are greater than those obtained in the fixed bed slow heating rate reactor. The liquids generated at a slow heating rate are of lower molecular weight, viscosity, and sulphur content, and of higher H/C atomic ratios compared with the liquids obtained in a rapid heating rate unit. The effect of increasing the maximum pyrolysis temperature (at a constant slow heating rate) was to increase the yield of light gases (mainly H) at the expense of char hydrogen content and char reactivity. The tar yield is not markedly influenced when the peak devolatilization temperature is increased at a relatively slow heating rate. However, the quality (as defined by the H/C (atomic) ratio) of the liquids, and the reactivity (in air) of char, was reduced when the peak pyrolysis temperature was increased. At a rapid heating rate, the primary products, which have many structural characteristics of the parent coal, are devolatilized. The quality of the liquids obtained at a rapid heating rate is, therefore, determined by the devolatilized primary coal fragments evolved at the devolatilization temperature. In a slow heating rate fixed bed unit, however, the primary coal fragments undergo additional cracking reactions which involve stabilization of free radicals by donatable hydrogen. This leads to the formation of low molecular weight hydrocarbons of relatively higher quality. In-situ (both intraparticle or extraparticle) stabilization of reactive coal fragments by donatable hydrogen may lead to a significant improvement in the overall quality of the pyrolysis liquids in a fixed bed system in which time-temperature history is conducive for such reactions.     

Pyrolysis of melamine–formaldehyde and urea–formaldehyde resins

Pyrolysis of melamine–formaldehyde and urea–formaldehyde resins in helium and air was investigated by means of TG and gravimetry with isothermal heating, as well as elemental and HCN analyses. Weight loss curves suggest three kinds of reactions involved in the pyrolysis, namely, initiation reactions, reactions splitting off volatile fragments, and reactions forming stabilized structures. In TG, in both helium and air atmospheres, the active weight loss of the melamine resin was completed in two steps, and that of the urea resin was completed in one step, which, however, consisted of a few small successive steps. The isothermal heating weight losses progressed through a few stages of first- and zeroth-order reactions. Arrhenius parameters were obtained for the weight losses in TG and with isothermal heating. The residue from the melamine resin is rich in carbon and nitrogen, and poor in oxygen and hydrogen, while that from the urea resin is rich in carbon, and poor in nitrogen, oxygen, and hydrogen. The effects of temperature on HCN yield changed, depending on the amount of air fed. The melamine resin evolved much more HCN than the urea resin because of the more stable C—N linkages in the resin.     

Sulfur removal from original and acid treated lignites by pyrolysis

Six original, three hydrochloric acid treated and three demineralized lignite samples were pyrolysed at seven different temperatures between 350 and 950 °C for 7 min under evolved gas atmosphere. All samples and their chars were analysed quantitatively for their total sulfur content and pyritic, sulfate and organic sulfur forms. The alkaline oxide contents of original lignites and their hydrochloric acid treated counterparts were determined. The results clearly indicate that calcium and sulfurous compounds in the parent lignites undergo various chemical changes during pyrolysis. The pyrolysis temperature, types of sulfur and calcium compounds, all affect the behaviour of sulfur during pyrolysis. Higher pyrolysis temperatures favour total sulfur removal for all lignites, reaching 30-54% around 850 and 950 °C. HCl treatment and demineralization decreases calcium contents, hence, increases quantitative sulfur removal from the lignites by pyrolysis. The maximum total sulfur removal from acid treated lignites is observed as 77%. The ratios of the total sulfur to heating value decreases with increases of pyrolysis temperature up to around 600 °C for acid treated lignites and no major changes are observed at higher pyrolysis temperatures; no common behaviour is observed for original lignites.     

炼焦煤尾煤热重动力学分析及热解产氢

基于热重分析和固定床热解实验,研究了升温速率和温度对高矿物质含量的炼焦煤尾煤热解特性的影响. 尾煤热解过程可分为室温至400, 400~600及600~950℃三个阶段. 尾煤与焦煤热解曲线基本吻合,尾煤热解特征温度略向高温区推移. 采用Coats-Redfern积分法拟合计算了尾煤热解的动力学参数,得出反应活化能为22.6~66.2 kJ/mol,热解过程可用3个二级反应描述. 30 g尾煤固定床实验结果表明,氢气在低于400℃析出很少,400~600℃缓慢析出,之后随温度升高析出增加,600℃后大量析出,900℃左右达到最大析出量. 终温950℃时,30 g尾煤热解产气4300 mL,氢气产量1722 mL;焦煤产气7950 mL,氢气产量2716 mL. 尾煤热解富氢气体产量达焦煤热解气产量的54%,具有较高的再利用价值.     

Effect of rank,temperatures and inherent minerals on nitrogen emissions during coal pyrolysis in a fixed bed reactor

Pyrolysis of 11 coals with carbon contents of 77–93 wt.% (daf) and corresponding demineralized samples has been studied in a fixed bed quartz reactor with a heating rate of 20 K/min to examine rank, demineralization, temperature and inherent mineral species dependences of nitrogen distribution. Nitrogen mass balances fall within 92.5–104.6%. The results indicate that the chars derived from the coals with higher rank show larger nitrogen retention. Demineralization suppresses volatile nitrogen emission during coal pyrolysis, especially for low rank coals. Coal-N conversion to tar-N reaches the asymptotic values at 600 °C. HCN yields are lower than NH₃ yields during coal pyrolysis. The trends in HCN and NH₃ emissions are very similar and the yields reach the asymptotic value at about 1200 °C. N₂ starts emitting at 600 °C, and as the temperature increases the conversion increases linearly with a corresponding reverse change of char-N. With the catalysts added, N₂ formation is prompted with the sequence of Fe>Ca>K>Ti≫Na≫Si≈Al, meanwhile, char-N decreases correspondingly. Fe, Ca, K, Na, Si and Al increase coal-N conversion to NH₃ with the sequence of Fe>Ca>K≈Na≫Si≈Al in the pyrolysis. Na addition prompts HCN formation; however, the presence of Ti and Ca decrease the HCN yields with small value. The other catalysts have no notable influence on HCN emission in the pyrolysis. Demineralization and Ti addition increase coal-N conversion to tar-N slightly whereas K, Ca, Mg, Na, Si and Al additions decrease tar-N yield weakly, other catalysts hardly influence tar nitrogen emission. N₂ emits mainly from char-N with slight contribution of volatile nitrogen. The mechanism of different N-containing species formation and catalysts influence in the pyrolysis is also discussed in the paper.