等离子体煤热解与气化工艺的研究进展

介绍了煤在热等离子体中转化为小分子化合物的2个重要过程,即等离子体煤热解和气化的基本原理、应用及发展状况。在非氧化性气氛中,煤热解生成的气体产物主要是乙炔、氢气、一氧化碳,此外还有甲烷和乙烯等小分子烃,乙炔的收率与煤种、粉煤粒度、反应器结构、粉煤进料方式、进料速度及操作条件密切相关,等离子体中氢的存在有利于乙炔的产生;在氧化性气氛中,煤气化产物主要是一氧化碳和氢气,煤中碳的转化率达95%,合成气体积分数约85%,二氧化碳体积分数低于5%。指出等离子体应用于煤转化过程是煤洁净利用的有效方式,具有潜在的工业化应用前景。     

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。     

低阶粉煤热解-气化一体化装置构想

为了实现《煤炭深加工产业示范"十三五"规划》中指出的研发清洁高效的低阶煤热解技术、攻克粉煤热解等关键技术及开发热解-气化一体化技术目标,通过阐述煤的热解和气化反应原理及目前普遍存在的热解、气化分产现实,提出了以分质产品、物料互给、热能循环、积木组合、塔状结构等为理念的一体化技术路线,并构想了一种双塔结构的低阶粉煤低温热解-气化一体化装置,介绍了该构想的理论基础、工艺流程、部件结构和主副塔组合方案。该构想装置可以将低阶粉煤分质生产出热解水蒸气、低温热解煤气、气化煤气、半焦等产品,为煤炭梯级延伸加工提供条件。     

Factors governing reactivity in low temperature coal gasification. Part II. An attempt to correlate conversions with inorganic and mineral constituents

Links between extents of coal gasification and the amounts and compositions of mineral components in coals have been investigated. The influence of demineralisation and impregnation with various inorganic components on the pyrolysis and CO₂-gasification behaviour of two coals have been examined at 0.1 and 1 MPa. The effect of mineral matter on pyrolysis and gasification behaviour has also been examined by correlating actual conversions of a calibration set of 23 coal samples with the mineral matter-related bands of their FT-IR spectra. Whilst mineral matter contents clearly affect conversions during gasification, results from this work show that it is difficult to find systematic patterns, regarding the effect of specific inorganic components in different coals. The prediction of catalytic activity from amounts and compositions of particular inorganic components appears unlikely to be feasible. These findings confirm the difficulty of relating information on original structural features of coals to weight loss during gasification.     

Volatilization behavior of fluorine in coal during fluidized-bed pyrolysis and CO2-gasification

The volatilization behavior of fluorine in five Chinese coals was investigated during fluidized-bed pyrolysis and CO₂-gasification at a temperature range of 500-900 °C. The effect of co-existed and added calcium on fluorine volatility during pyrolysis was also determined. With increasing pyrolysis temperature, the volatility of fluorine increases. However, the volatility is greatly dependent on the fluorine chemical forms occurred in coal. Except for Datong and Zhungeer coal, more than 65% of fluorine in other three coals occurs as the steady forms. Fluorapatite is not the major carrier of fluorine in the coals studied. Fluorine volatility is retarded by coexisting calcium during coal pyrolysis, indicating that at least part of the stable forms of fluorine in coal might occur as calcium fluoride or calcium fluoride with complex compounds which are stable even at high pyrolysis temperature. The addition of CaO and limestone can suppress the release of fluorine during pyrolysis. The effect of CaO is better than that of limestone. The volatility of fluorine of coal during CO₂-gasification depends on not only the occurrence mode of fluorine, but also the gasification reactivity of the coal. Compared with N₂ atmosphere, CO₂ is more favorable to the release of fluorine from coal.     

恩德粉煤气化炉的气化工艺及应用

煤气化技术对于促进煤炭的综合利用、改善当前资源紧缺状况并减少环境污染具有重要的意义。对恩德粉煤气化炉的特点和气化工艺流程、工艺操作进行了分析,并以景德镇市焦化煤气总厂应用恩德粉煤气化炉实现煤气化的工程实例,分析了恩德粉煤气化技术的运行指标和投资效益。     

低温氧化破粘对煤炭地下气化热解特性的影响

粘结性烟煤在地下气化过程中容易造成通道堵塞,气流分布不均匀进而导致地下气化过程环境的恶化,使气化反应停止。粘结特性在热解过程中表现得尤为突出,研究了低温氧化破粘的方法对地下气化热解特性的影响。结果表明随着氧化时间的增加,最大失重速率降低,煤气中H2,CH4体积分数以及热值在部分热解温度区间均低于原煤,从而增加了煤炭地下气化热解惰性。     

Reactivity and structural change of coal char during steam gasification

This study is intended to clarify the relationship among the reactivity of coal char with steam, structural change in residual carbon, and ash behavior. Steam gasification of various coal chars and demineralized chars was carried out in a fixed-bed reactor. After gasification, the reacted char was analyzed using laser raman spectroscope (LRS), and scanning electron microscope, energy dispersive X-ray spectroscope (SEM/EDX) mapping. Results of SEM images and EDX-mappings revealed that novel parallel analysis of cross correlation between EDX-mapping and LRS-mapping was found to be very effective for the comprehensive evaluation of ash behavior and carbonaceous structure. As the gasification reaction proceeds, the reactivity of the char was varied; existence of Si and Al seemed to suffocate the char reactivity.     

城市生活垃圾热解气化技术研究进展

从城市生活垃圾热转化方式的比较入手,简要阐明了热解气化过程,讨论了各类热解气化反应器的优缺点,概述了城市生活垃圾热解、气化实验研究进展以及热解气化技术中试及应用情况。通过比较各类实验研究,明确了热解温度、加热速率对热解产物产量及产物分布的影响,气化温度、氧气当量比(RO)对含氧气化反应的影响,气化温度、水蒸气与城市生活垃圾质量比(S/M)对水蒸气气化反应的影响。指出了城市生活垃圾热解气化实验研究热点在于优化控制参数,提高反应速率,促进目标产物高值化,抑制其它产物及污染物的生成,以及城市生活垃圾热解气化技术的发展方向。     

Fundamentals of coal topping gasification: Characterization of pyrolysis topping in a fluidized bed reactor

Coal topping gasification refers to a process that extracts the volatiles contained in coal into gas and tar rich in chemical structures in advance of gasification. The technology can be implemented in a reactor system coupling a fluidized bed pyrolyzer and a transport bed gasifier in which coal is first pyrolyzed in the fluidized bed before being forwarded into the transport bed for gasification. The present article is devoted to investigating the pyrolysis of lignite and bituminite in a fluidized bed reactor. The results showed that the highest tar yield appeared at 823 to 923 K for both coals. When coal ash from CFB boiler was used as the bed material, obvious decreases in the yields of tar and pyrolysis gas were observed. Pyrolysis in a reaction atmosphere simulating the pyrolysis gas composition of coal resulted in a higher production of tar. Under the conditions of using CFB boiler ash as the bed material and the simulated pyrolysis gas as the reaction atmosphere, the tar yields for pyrolytic topping in a fluidized bed reactor was about 11.4 wt.% for bituminite and 6.5 wt.% for lignite in dry ash-free coal base.     

Distribution of volatile sulphur containing products during fixed bed pyrolysis and gasification of coals

Three sub-bituminous and two bituminous coals from Western Canada were used to study the evolution of H₂S, COS and SO₂ during the pyrolysis and gasification processes in a fixed bed reactor. For all types of coals, most of H₂S and SO₂ were released during the devolatilization stage. COS was formed only during the gasification stage in the presence of CO₂. The mineral matter of coal may have played a role during the gasification stage. Some observations made during this latter stage in CO₂ and/or steam were interpreted in terms of the equilibrium effects.     

气化对煤质的要求

介绍了气流床气化对煤质的要求,论述了煤的水分、反应活性、粒度和灰分对气化的影响。研究表明,煤的内水含量是决定煤浆性能的主要因素,灰渣的黏温曲线比灰熔点对气化炉的操作更具指导意义,选择在操作温度区间灰渣黏度变化平缓的煤种有利于气化炉的安全、平稳运行。     

Coal pyrolysis and gasification in a fluidized bed thermogravimetric analyzer

The kinetics and modelling of coal gasification were studied in the newly developed fluidized bed thermogravimetric analyzer. The total weight loss obtained from the fluidized bed reactor and the total gas product are in general agreement. The presented model for the micro‐fluidized bed reactor encompasses the kinetics of coal pyrolysis as well as the gasification reactions. For coal pyrolysis, the resulting activation energies for the individual gases were 34.7 to 59.8 kcal/mol. These values are 19 to 21 % lower than those found in the literature for similar coals. This decrease of the activation energies of the endothermic pyrolysis reactions is attributed to a gradient of temperature of 185 to 209 °C. The obtained activation energy for the CO shift reaction is 46.6 kcal/mol, increasing by 20 % from the one used in the literature. This increase of the activation energy of such a mildly exothermic reaction represents an equivalent of 170 °C gradient of temperature. The effects of temperature on the yield and the composition of the gas product are studied. Experimental results and equilibrium data are also compared. The model shows reasonably good agreement with the experimental results, except for the water gas shift reaction.

     

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.     

Transformation of arsenic in Yima coal during fluidized-bed pyrolysis

Arsenic is one of the most concerned trace elements in coal because of its toxicity and environmental persistence. Little information about the transformation behavior of arsenic under pyrolysis conditions was reported. In this paper, the volatilization behavior of arsenic and the influence of coexisting mineral matters and additive CaO were investigated during pyrolysis of Yima coal in a fluidized-bed reactor at temperatures ranging from 350 to 900 °C. The modes of occurrence of arsenic in Yima raw coal and its two char samples are determined using four methods including density fractionation, demineralization, X-ray diffraction (XRD) and sequential chemical extraction. It is found that arsenic in Yima coal is mainly associated with pyrite, and changes greatly during coal pyrolysis. Staged volatility behavior of arsenic is observed during Yima coal pyrolysis. From 350 to 500 °C, arsenic volatility increases with increasing temperature, while it changes little from 500 to 800 °C. Arsenic behavior in YimaD (demineralized sample of Yima) and CaO additive reveal that the vaporization of arsenic in Yima coal during pyrolysis is retarded by its coexisting mineral matters or added CaO to form thermally stable forms of arsenic. These forms might be generated through the formation of As-Ca complexes such as calcium arsenate, or through absorption and capture reactions with aluminosilicate mineral matters and trapped into their lattices.     

Trace element evaporation during coal gasification based on a thermodynamic equilibrium calculation approach

Thermodynamic equilibrium calculations using the HSC-Chemistry program were performed to determine the distribution and mode of occurrence of potentially toxic and corrosive trace elements in gases from coal gasification processes. The influence of temperature, pressure and gas atmospheres on equilibrium composition was evaluated. In these reducing conditions, the behaviour of the trace elements is complex, but some form of organization can be attempted. Elements were classified into three groups. Group A includes those elements that, according to thermodynamic data at equilibrium, could probably be condensed in coal gasification. Mn is classified in this group. Group B contains those elements that could be totally or partially in gas phase in gas cleaning conditions, and can be divided into two subgroups, depending on whether the cleaning conditions are hot or cold. Co, Be, Sb, As, Cd, Pb, Zn, Ni, V, Cr are elements in this group. Group C contains those elements that could be totally in gas phase in all the possible conditions, including flue gas emissions. Se, Hg and B are the elements that make up this group.     

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。     

CO2 gasification of wood charcoals derived from vacuum and atmospheric pyrolysis

The gasification of biomass derived char obtained via vacuum and atmospheric pyrolysis of Populus tremuloides has been studied in the ranges of 725–960°C and 0.1 to 6 MPa. CO₂ was used as the oxidizing gas. The results show that char reactivity is influenced by the preheating rates and that pressure effects are significant between 850°C and 950°C. A correlation based on the expression: df/dt = k₀{exp(-E/RT)}(1 - f)^af^βP^yCO₂ was used to fit the experimental data. In general, vacuum pyrolysis derived char showed a higher reactivity than atmospheric pyrolysis chars. An explanation based on a higher oxygen content of the vacuum pyrolysis char is suggested.     

Numerical study on the coal gasification characteristics in an entrained flow coal gasifier

The coal gasification process of a slurry feed type, entrained-flow coal gasifier was numerically predicted in this paper. By dividing the complicated coal gasification process into several simplified stages such as slurry evaporation, coal devolatilization and two-phase reactions coupled with turbulent flow and two-phase heat transfer, a comprehensive numerical model was constructed to simulate the coal gasification process. The k– turbulence model was used for the gas phase flow while the Random-Trajectory model was applied to describe the behavior of the coal slurry particles. The unreacted-core shrinking model and modified Eddy break-up (EBU) model, were used to simulate the heterogeneous and homogeneous reactions, respectively. The simulation results obtained the detailed information about the flow field, temperature and species concentration distributions inside the gasifier. Meanwhile, the simulation results were compared with the experimental data as a function of O₂/coal ratio. It illustrated that the calculated carbon conversions agreed with the measured ones and that the measured quality of the syngas was better than the calculated one when the O₂/coal ratio increases. This result was related with the total heat loss through the gasifier and uncertain kinetics for the heterogeneous reactions.     

Dynamics of trace elements release in a coal pyrolysis process

Samples of coal and solid carbonization product obtained at four temperatures: 400, 600, 850 and 1000 °C were tested on account of the contents of trace elements. The following hazardous trace elements were considered: arsenic, beryl, cadmium, manganese, nickel, lead, mercury and selenium. The release curves for the elements tested were determined.