煤系针状焦原料预处理技术进展

针状焦是生产超高功率石墨电极的新型材料。据针状焦成焦机理,煤焦油和煤焦油沥青作为针状焦生产原料时必须进行预处理将其中的喹啉不溶物等杂质除去。煤系针状焦原料的预处理方法主要包括溶剂法、过滤法、离心分离法、加氢法、改质法及溶剂-加氢法。上述方法均可将煤焦油和煤焦油沥青中的喹啉不溶物降至满足针状焦生产的要求,其中溶剂法中的溶剂-沉降法现已得到工业化应用。     

Puffing inhibitors for coal tar based needle coke

The efficiency of various puffing inhibitors has been studied systematically using carbon samples prepared from coal tar based needle coke. Puffing was reduced by the addition of nickel and cobalt oxides. The bulk density of moulded blocks subjected to graphitization was increased also by the addition of these oxides, because of their catalytic ability for carbonization. No sulfide was observed during the graphitization process, implying that puffing inhibition is not necessarily due to the reaction of metals with sulfur compounds in cokes. The interlayer spacing of needle cokes mixed with effective puffing inhibitors was considerably decreased during graphitization. The action of puffing inhibitors seems to change the timing between the gas evolution and the softening of carbon bodies.     

芳香族硝基化合物改性煤沥青研究

以煤沥青为原料,通过添加不同含量的芳香族硝基化合物对煤沥青进行改性处理,采用TG、CO2反应性、XRD和SEM对改性沥青焦进行表征。结果表明,芳香族硝基化合物有效地促进了煤沥青在炭化过程中的焦化缩聚,使产物沥青焦结构更加致密,并在一定程度上改变了沥青焦的氧化行为,从而显著提高了沥青黏结焦的抗氧化性能。     

石油焦对生物质气化中焦油裂解的影响

引言 生物质作为一种清洁可再生能源正在受到世界各国的重视.生物质气化是生物质高品位利用的一种主要技术,但在气化过程中产生的焦油对装置的长周期平稳运行有严重危害,一方面低温时焦油易凝结为黏稠的液体,与灰粒一起堵塞输气管道;另一方面焦油的存在还会降低气化效率[1-6],这在一定程度上影响了生物质气化技术的推广应用,因此有必要采取措施降低气化气中的焦油量.     

Carbonization of hydrogenated ethylene tar pitch; study of the pitch molecular compactness factor and coke optical texture

Compactness factors of aromatic molecules in hydrogenated ethylene tar pitch were calculated as a parameter to relate to properties of mesophase of the carbonization system. Compactness factors, φ, derived from structural analyses of hydrogenated ethylene tar pitch were also related to the size and shape of optical textures of resultant cokes. Hydrogenated ethylene tar pitches having values of φ 〉 0.5 gave cokes with flow type anisotropy and relate to formation of peri-condensed structures. The spin-lattice relaxation times, T₁, for the cokes derived from hydrogenated ethylene tar pitch, are related to their optical texture.     

Graphitization behavior of hydrogenated ethylene tar pitch

The graphitization behavior of cokes prepared from ethylene tar pitch (ETP) hydrogenated at temperatures from 473 to 673 K has been studied by magnetoresistance measurements at liquid nitrogen temperature and by scanning electron microscopy. Graphitization heat treatment of the cokes was carried out at 3273 K. Hydrogenation temperatures of 473 and 523 K resulted in graphitized cokes with random layer plane textures and low degrees of graphitization. Hydrogenation at higher temperatures was effective in promoting development of flow-type textures during graphitization. The coke from ETP hydrogenated at 673 K showed the highest graphitizability, preferred orientation and flow-type texture developed by heat treatment.     

Anomalous capillary flow of coal tar pitches

Capillary flow of liquid coal tar pitch into a coke bed was studied. Anomalies in the flow could not be attributed to a plugging effect for mesophase content lower than 20 wt%. The flow behaviour of small pitch droplets can be correlated with the change in physicochemical properties, as measured by the glass transition temperature, on penetration into the coke bed.     

Possibilities of tar addition to coal as a method of improving coke strength

Tests carried out in a pilot oven, in individual 19-t ovens and for a short time, in a 4.5 m high 54 oven battery, showed that addition of a certain amount of tar directly to any coal mix can improve the coke properties. The experimental procedure adopted for tar addition and the determination of the coke properties are highlighted.     

Carbonization behavior of hydrogenated ethylene tar pitch

Carbonization behavior of ethylene tar pitch has been studied with respect to mesophase formation by means of modification of the chemical composition of the starting materials. The hydrogen treatment of ethylene tar pitch has been carried out over the temperature range from 473 to 673 K under a pressure of 10 MPa without catalyst. Then, the hydrogenated ethylene tar pitches were carbonized at 723 K and the optical texture of the resultant cokes were assesed by optical microscopy. It was revealed that the carbonization of the ethylene tar pitch hydrogenated at 673 K gives a coke of optical texture with enlarged flow-domain. The hydrogen-transfer ability of the ethylene tar pitches during the temperature range of mesophase formation was estimated by the method of 9,10 dihydroanthracene (DHA) formation through co-carbonization of the pitch with anthracene. It was recognized that the larger the amount of conversion of DHA, the better is the development of optical texture.     

Needle coke formation derived from co-carbonization of ethylene tar pitch and polystyrene

Ethylene tar pitch was co-carbonized with waste polystyrene to prepare needle coke. The modified properties of mesophase, which were greatly improved due to increasing naphthenic and other alkyl content, availed the formation of needle coke with high quality. The coefficient of thermal expansion value was decreased from 3.2 × 10⁻⁶/°C to 0.3 × 10⁻⁶/°C and the optical texture of the coke was changed from coarse mosaic texture to flow domain of high uniaxial orientation after adding waste polystyrene into ethylene tar pitch. The low viscosity of the mesophase pitches favored the development of mesophase and highly uniaxial arrangement. The increase in alkyl group content greatly improved characteristics of the needle coke.     

Interaction between a coke and a tar. 1. Influence of the surface chemical functions of coke

The authors studied the relation between oxygen-containing functions of cokes and contact angles of tars on cokes. Using two different cokes, a coal-tar pitch and polymer models, they showed that the coke-tar interactions depend on the hydrogen bonding between the two components and that above a critical value surface-chemical-function content has no influence on coke-tar interactions.     

Molasses and air blown coal tar pitch binders for the production of metallurgical quality formed coke from anthracite fines or coke breeze

The effect of the type and the amount of hardeners, such as ammonium nitrate, ammonium carbonate and nitric acid on the molasses bonded briquettes prepared from anthracite fines or coke breeze were investigated. Amongst the hardener studied the best results were obtained with 2.5% ammonium nitrate hardener. The briquettes produced with this hardener were highly water resistant but not waterproof and their tensile strengths were not adequate to be used as a substitute for the metallurgical coke. Therefore, the briquettes were prepared with molasses containing 2.5% ammonium nitrate hardener and air blown coal tar pitch blended binder. When the blended binder was used for the production of anthracite fines or coke breeze briquettes, after curing at 200 °C for 2 h, they became waterproof and their tensile strengths were found to be sufficient to be used as a substitute for coke oven coke. The briquettes after curing could be directly charged into the blast furnace without carbonizing them at high carbonization temperatures. Since molasses and coal tar pitch, are relatively cheap and readily available materials, the process investigated could be economical way of producing high quality formed coke.     

Modification of petroleum coke by different additives and the impact on anode properties

Anodes, which provide the carbon required for aluminum production, are made from dry aggregates (petroleum coke, rejected anodes, and butts) with coal tar pitch as the binder. Good quality anodes require good interaction between coke and pitch, and this relies on good wetting properties. The objectives of this work are to analyze the wetting properties of four different cokes with and without modification using an additive and to test the effect of the modified coke on anode properties. A FTIR study was done to identify functional groups in non‐modified and modified coke samples since they play an important role on coke‐pitch interactions. The wetting tests were done using the sessile‐drop method to measure the contact angle between coke and pitch. The results showed that the additive improved the wettability of all four cokes by pitch. The least wettable coke was chosen to produce anodes. For anode production, the entire dry aggregate is modified. The additive was mixed with the dry aggregate using two different approaches (one day earlier and 5 min before mixing). The anodes were characterized before and after baking. The early treatment with the additive was found to be better for the modification of dry aggregate.

     

针状焦用煤沥青的调制研究

介绍了煤系针状焦用原料的要求及调制方法,讨论了2种工业上原料精制的工艺,并重点阐述了国内外对原料的组分、反应性、软化点、流变性、残炭值和结晶度等方面的改性研究进展。在此基础上对煤沥青调制研究在国内的发展前景进行了展望。     

The strength of industrial cokes. 5. Influence of coke breeze in a coal charge on tensile strength of coke

The purpose of this study was to determine the influence of different proportions and different particle sizes of coke breeze in a coke-oven charge on the tensile strength of the coke. The diametrical-compression test was used to determine the tensile strength of the coke produced in a 10-t test oven and the results obtained were considered in relation to the composition of the oven charge, the coke micum indices and to parameters describing the coke texture. It was established that breeze additions caused measurable but nonsystematic changes in the coke tensile strength and that decreasing the breeze particle size generally increased the coke tensile strength. These changes could not however be directly related to changes observed in the density, porosity, pore-wall thickness or mean pore size of the cokes. The previously established relations between micum indices and the tensile strength of foundry cokes were also found to be inapplicable. The conclusion was drawn that the behaviour described is associated with some, at present unestablished, factor of the blend composition, one possibility being the relative proportions and compatibility of the ‘binder’ and inert material acting through their influence on those aspects of the coke microstructure which control the coke breakage.     

焦炉上升管中煤焦油流动特性的实验研究

为除去焦炉荒煤气显热回收过程中冷凝结焦在换热管壁表面的煤焦油,以煤焦油高温黏温特性曲线为实验依据,研究了200~800℃煤焦油在普通碳钢管道表面和镀镍涂层管道表面的流动特性情况,并线性拟合出煤焦油流动特性随温度变化的关系方程。结果表明:温度与换热管道表面煤焦油的流动特性之间呈现很好的指数关系;当管壁温度达到400℃左右时,普通碳钢管道表面的煤焦油由于流动特性的改变而基本脱除干净,镀镍涂层管道的温度在350℃左右;镀镍涂层管道在抑制结焦方面明显优于普通碳钢管道,其抑制结焦率在20%左右。     

Kinetic model of low temperature coal tar hydrocracking in supercritical gasoline for reducing coke production

To reduce coke production during low temperature coal tar hydrocracking in supercritical gasoline, a lump kinetic model was derived on the basis of catalytic cracking reaction mechanism. Lumps were defined by different reaction properties. Reaction rate constants, indexes of hydrogen to coal tar ratio, indexes of gasoline to coal tar ratio, activation energies, and pre-exponential factors were estimated according to the previous experimental data. The results show that the proposed model could not only predict the product yields successfully, but also provide more information which was useful for any attempts to reduce the coke content and promote the conversion of coal tar to light oils.     

Carbonization of coal blends: mesophase formation and coke properties

Laboratory investigations of strength of cokes from blends of coals incorporating pitch were supported by 7 kg trials. The stronger cokes showed a greater interaction between coal and pitch to produce an interface component of anisotropic mozaics which is relatively resistant to crack propagation. The process whereby coal is transformed into coke includes the formation of a fluid zone in which develop nematic liquid crystals and anisotropic carbon which is an essential component of metallurgical coke. Strength, thermal and oxidation resistance of coke can be discussed in terms of the size and shape of the anisotropic carbon which constitutes the optical texture of pore-wall material of coke. Coals of different rank form cokes with different optical textures. Blending procedures of non-caking, caking and coking coals involve the interactions of components of the blend to form mesophase and optical texture. Petroleum pitches used as additives are effective in modifying the carbonization process because of an ability to participate in hydrogen transfer reactions.     

Catalytic reforming of tar during gasification. Part I. Steam reforming of biomass tar using ilmenite as a catalyst

Ilmenite, a natural iron-containing mineral, has been investigated as an inexpensive catalyst for the steam reforming of volatiles (tar) from the pyrolysis of mallee woody biomass. The results indicate that ilmenite has good activity for the steam reforming of tar into gases due to its highly dispersed iron-containing species. The supply of external steam, in addition to the H₂O and CO₂ produced during the pyrolysis of biomass, plays an important role in minimising the formation of coke on the catalyst surface and thus the catalyst activity. The catalyst deactivation due to coke formation has more adverse effects on the reforming of larger aromatic ring system with steam than that of smaller ones. In addition, the supply of additional oxygen at low concentration changed the outcomes of tar reforming mainly because oxygen activated the smaller aromatic ring systems and polymerised them into larger aromatic ring systems in the gas phase.     

Production of isotropic coke by thermocracking of the anthracene fraction of coal tar

The properties of coke obtained by heat treatment of the anthracene fraction of coal tar under pressure (by thermocracking) are investigated. Pressures up to 5 MPa are used; the temperature is 500 or 550°C. For comparison, pitch coke is obtained from oxidized pitch with softening temperatures of 166.2 and 190.2°C. The coke yield from thermocracking is 70–75%. The following properties of the coke are determined: the actual density, the ash content, the yield of volatiles, the optical microstructure, the elementary composition, the change in volume on heating to 2400°C, the impurity composition, and the X-ray structural characteristics. High temperatures (at least 550°C) and heating rate of the anthracene fraction facilitate the formation of a large quantity of active radicals, which instantaneously form the three-dimensional coke structure, preventing the growth and coalescence of mesophase particles; isotropic coke is formed, with a microstructure score of 2.2. At 500°C, anisotropic coke is formed, with a microstructure score of 4.3. Despite the high softening temperature and the content of the α1 fraction, the high-temperature pitch does not form isotropic coke on carbonization. The macrostructure of the coke obtained by thermocracking is monolithic, with fine pores. The thermocracking conditions (temperature, pressure, presence of H₂) facilitate partial destruction and hydrogenation of the heterocyclic compounds. As a result, the coke has a reduced N, S, and O content. For pitch coke, the nitrogen content is 20–40% higher. The lack of ash in the anthracene fraction of coal tar results in ash- and metal-free coke. The coke obtained by thermocracking also has satisfactory X-ray structural characteristics and undergoes practically no expansion on graphitization, in contrast to pitch coke. In view of the technological convenience (absence of liquid products, high coke yield) and the quality of the coke, the production of isotropic coke by thermocracking may be regarded as a promising means of supplying the raw material used to produce artificial graphite.