Predictive equations for CO2 emission factors for coal combustion, their applicability in a thermal power plant and subsequent assessment of uncertainty in CO2 estimation

The emission of carbon dioxide varies systematically with the rank and type of coal combusted. Hence use of a single default emission factor proposed by IPCC (Inter Governmental Panel on Climate Change) for entire categories coals may not be appropriate option to obtain a reliable estimate of carbon dioxide emission level or towards the preparation of national carbon dioxide inventory. Even predictive equations developed based on the coals of different origin may not work well with coals of a specific origin. Several linear predictive equations were thus developed separately for coking and non-coking coals of Indian origin for the estimation of carbon dioxide emission utilizing basic coal parameters such as VM, FC, GCV and NCV on different basis. Large numbers of authenticated data set were used for multiple regression analysis and good correlations were obtained. Those equations were also validated with different data sets of Indian coals. Its applicability towards estimation of CO₂ emission from power plant was also studied and uncertainty in CO₂ estimation is revealed. The developed equations may be utilized to get a realistic estimate of carbon dioxide emission with specific cases where Indian coals are mostly used.     

The nature of coking coals

A review of the properties and the structure of coals occupying the middle position in the coalification scale that show the best coking properties — gas coals, gas-coking coals, ortho, meta and semi-coking coals — with particular regard to their behaviour on heat treatment is presented. Problems of coking coals as components of blends in the production of metallurgical coke, as component and binding agent in the process of obtaining metallurgical formed-cokes, and the utilization of coking coals and their extracts as raw materials in the electrode industry, are discussed. The classification of coking coals and questions still to be solved concerning the origin, properties, structure and rational utilization of coking coals, are commented on.     

A laboratory scale assessment of the utilization potentials of sub-bituminous Nigerian coals as components of coking blends

This paper examines the ability of A240 Petroleum pitch to improve the coking characteristics of sub-bituminous Lafia and Enugu coals of Nigeria. Also examined is the compatibility of Enugu and Lafia coals with a prime coking Ogmore coal in a blend for coke making. The exercise is motivated by the desire to include non-coking Nigerian coals in coal blends for making blast furnace coke.The coking characteristics of Lafia and Enugu coals are highly susceptible to improvement by A240 petroleum pitch. The pitch also interacts with the improves the coking characteristics of a blend of Enugu and Lafia coals.No interaction occurs between Enugu and Ogmore coals. Little interaction occurs between Lafia and Enugu coals. A strong interaction occurs between Lafia and Ogmore coals. Ogmore coking coal tremendously improves the coking characteristics of a blend of Lafia Enugu coals. Optical microscopy, microstrength and reactivity tests reveal that high volatile coking Lafia coal act as a bridging coal between Enugu coal and a prime coking coal in a ternary coking blend.     

Structural analysis of quinoline and pyridine extracts of coals

Various ranks of coals were extracted in an autoclave with quinoline at 350–380°C for 1–4 h. More than 50% of bituminous coals were dissolved, and almost 100% of Japanese bituminous coals in particular were dissolved. These quinoline extracts were further extracted by shaking with pyridine at room temperature for 8 h and the extraction yield attained a maximum of 85%. NMR spectra of these extracts were recorded using deuteroquinoline and deuteropyridine as solvent. The structural indices calculated from the observed spectra showed a good agreement between quinoline extracts and pyridine extracts, which indicates that the coal structure is almost homogeneous. The aromatic ring number in structural units varied from 1–2 in younger coals to 5 in coking coals. f_a increased from 0.7 for younger coals to 0.9 for coking coals. The aliphatic carbon number per structural unit increased from younger to older coals, but foreign coals had smaller values than Japanese coals, which corresponds well with higher values of H/C in Japanese coals.     

Coal characterisation by automated coal petrography

Automated imaging techniques were refined to characterise the rank and maceral composition of coals by a full maceral reflectogram of polished coal grain mounts. Precision was improved by processing individual grains in each image separately and correcting within the software for the topography that occurs between the different macerals and minerals in the grains. Maceral group proportions and vitrinite reflectance information extracted from these reflectograms compared well with manual results for a comprehensive suite of Australian coals varying in rank from a mean vitrinite reflectance of 0.48-2.13%. A parameter that combines rank and type calculated from the reflectograms correlated strongly with chemical properties determined by ultimate and proximate analyses. For a limited number of samples, for which coking tests had been performed, this parameter also correlated with estimated coking performance.     

Influence of the permeability of the coal plastic layer on coking pressure

Ten coals of different rank and coking pressure characteristics were chosen in order to study the time of occurrence of the phenomena that take place during the coking of a coal and the way they affect the generation of dangerous coking pressures. Parameters derived from thermoplastic, thermogravimetric and permeability tests were studied together with semicoke contraction and the coking pressure generated by the coals in a movable wall oven. It was found that for safe coals, the maximum evolution of volatile matter occurs near the temperature of maximum fluidity. The position of the maximum rate of volatile matter evolution with respect to the zone of low permeability varies depending on the coking pressure characteristics of the coals. In addition, the relationship between the period of low permeability to the resolidification temperature may serve to indicate the degree of dangerousness of a coal. The fissure pattern of the semicoke was found to be related to the coking pressure and semicoke contraction.     

Influence of thermoplastic properties on coking pressure generation: Part 1 - A study of single coals of various rank

In this study a number of high coking pressure coals with different fluidities were evaluated alongside a number of low pressure coals also with differing fluidities. This was to confirm findings from an earlier study using a limited selection of coals, and to establish rheological parameters within which a coal may be considered potentially dangerous with regards to coking pressure. The results have confirmed and elaborated on previous findings which show that parallel plate displacement (ΔL) and axial force profiles can be used to distinguish between high and low pressure coals, with peak values indicating cell rupture and subsequent pore network formation. This is thought to correspond with plastic layer compaction in the coke oven.For low pressure coals pore coalescence occurs quite early in the softening process when viscosity/elasticity are decreasing and consequently a large degree of contraction/collapse is observed. For higher pressure coals the process is delayed since pore development and consequently wall thinning progress at a slower rate. If or when a pore network is established, a lower degree of contraction/collapse is observed because the event occurs closer to resolidification, where viscosity and elasticity are increasing. For the higher fluidity, high coking pressure coals, a greater degree of swelling is observed prior to cell rupture, and this is considered to be the primary reason for the high coking pressure observed with these coals. An additional consequence of these events is that high pressure coals are likely to contain a higher proportion of closed cells both at and during resolidification, reducing permeability in both the semi-coke and high temperature plastic layers, respectively.Using a rheological mapping approach to follow viscoelastic changes during carbonisation it has been possible to identify specific regions associated with dangerous coals. These tend to be fusible coals where at the onset of expansion, δ (elasticity) < 54° and η* (complex viscosity) > 5 × 10⁵ Pa s, and where in most cases δ_MAX does not exceed 65°.     

Investigation of the chemical structures of coking and non-coking coals in original and reductively alkylated solid states via 13C n.m.r. and i.r. spectroscopies

Chemical structures of four Turkish coals in original and reductively alkylated forms were investigated in the solid state by CP/MAS ¹³C n.m.r. and i.r. spectroscopies. Dilatation properties of these samples were also determined. It was observed that, while the aliphatic parts of the coking coals are mainly composed of short and straight alkyl groups and alicyclic structures, the aliphatic parts of the non-coking coals are to a larger extent composed of branched chains and/or alicyclic structures. It was concluded that ether bonds linking aromatic units are more prominent in the coking coals, whereas in the non-coking coals aromatic-O-aliphatic and/or alicyclic ethers dominate. The degree of condensation of aromatic structures was found to be higher in the coking coals, and the extent of reductive alkylations was higher in comparison with the non-coking coals. Non-coking coals were found to be alkylated preferentially at their phenolic oxygens. Difference spectra were found to be very useful in following organic chemical structural changes that accompany reductive alkylation.     

Interactions between coking coals in blends

The thermoplastic behaviour of 78 binary blends of Australian coking coals was measured using proton magnetic resonance thermal analysis. Their measured extents of fusion were compared with the values calculated from measurements made on the component coals assuming additivity. Significant differences between calculated and measured results were found for most blends, though only at temperatures between 400 and 520 °C: the coals interacted at these temperatures in a way that affected their fluidity. Both positive and negative differences were observed. The magnitude of the differences increased both with increasing differences in rank between the coals and differences in fluidity between the coals. A statistical study of the differences showed that material that became fluid in coal at temperatures below about 360 °C did not appear to contribute to the interactions, which suggests that fluid material derived from liptinite plays a much smaller role in interactions than fluid material derived from vitrinite or inertinite. Additionally, the study indicated that the less fusible material in a blend slightly reduced the extent to which the associated more fusible material fused. It was not acting as an inert diluent.Fifteen blends of six Argonne premium coals were examined to see if the relationships found for Australian coals between the magnitude of the interaction and coal properties could be generalised. In most cases the agreement was good. However, at some temperatures, blends of Upper Freeport coal with lower rank coals were far less fluid than expected, suggesting that the fluidity of Upper Freeport coal is especially sensitive to these low rank coals.The general effect of interactions between coals of different ranks was to narrow the thermoplastic temperature range of the blend without reducing the maximum fluidity, in effect making the thermoplastic profile of the blend resemble the profile expected from an individual coal of the same average rank as the blend. The interactions are attributed to transfer of plasticising volatile material between the coals.     

Correlation of microstrength and industrial drum strength indices of metallurgical cokes

Correlations between microstrength and industrial drum strength indices of metallurgical cokes were obtained using a 230 kg coke oven. Twelve coking coals from different countries, and ranging in ASTM rank from hvA to Iv bituminous, were carbonized singly and in blends. Microstrength, JIS Drum and ASTM Drum tests were performed on the cokes produced. The results indicated that the relationship between the Dl¹⁵⁰₁₅ index and microstrength was non-linear. Correlation coefficients increased when highly fluid US hvA bituminous coals were excluded. The relationship between ASTM hardness and microstrength was less defined. Results of this study indicate that thermoplasticity is an important consideration when correlating microstrengths with industrial drum strengths.     

Speciation and thermal transformation of sulfur forms in high-sulfur coal and its utilization in coal-blending coking process:A review

The utilization of high-sulfur coal is becoming more urgent due to the excessive utilization of low-sulfur,high-quality coal resources, and sulfur removal from high-sulfur coal is the most important issue. This paper reviews the speciation, forms and distribution of sulfur in coal, the sulfur removal from raw coal,the thermal transformation of sulfur during coal pyrolysis, and the sulfur regulation during coal-blending coking of high organic-sulfur coals. It was suggested that the proper characterization of sulfur in coal cannot be obtained only by either chemical method or instrumental characterization, which raises the need of a combination of current or newly adopted characterization methods. Different from the removal of inorganic sulfur from coal, the organic sulfur can only be partly removed by chemical technologies;and the coal structure and property, particularly high-sulfur coking coals which have caking ability,may be altered and affected by the pretreatment processes. Based on the interactions among the sulfur radicals, sulfur-containing and hydrogen-containing fragments during coal pyrolysis and the reactions with minerals or nascent char, regulating the sulfur transformation behavior in the process of thermal conversion is the most effective way to utilize high organic-sulfur coals in the coke-making industry.An in-situ regulation approach of sulfur transformation during coal-blending coking has been suggested.That is, the high volatile coals with an appropriate releasing temperature range of CH_4 overlapping well with that of H2 S from high organic-sulfur coals is blended with high organic-sulfur coals, and the C–S/C–C bonds in some sulfur forms are catalytically broken and immediately hydrogenated by the hydrogencontaining radicals generated from high volatile coals. Wherein, the effect of mass transfer on sulfur regulation during the coking process should be considered for the larger-scale coking tests through optimizing the ratios of different coals in the coal blend.     

Optical anisotropy of carbonized coking- and caking-coal vitrains

The purpose of this work was to characterize in detail the optical anisotropy formed during carbonization of the range of coals used in the coking industry, the ultimate objective being to attain a better understanding of the coking process. Vitrains hand-picked from a series of coking and caking coals were carbonized to various temperatures between 380 and 1000 °C. The semicokes and cokes so produced were examined by polarized-light microscopy to determine the proportions of the different types of optical anisotropy developed during carbonization. The results demonstrated that coals normally grouped within one class of the coal classification system used by the National Coal Board can lead to cokes which are significantly different in terms of their optical anisotropy. The process of the anisotropic development during carbonization can be explained generally in terms of loss of volatile matter, variations in viscosity of the plastic mass, and distortion of ordered phases by the pressure of evolving gases. Differences in carbonization behaviour as judged by the coke anisotropy can be attributed to differences in the ‘molecular-structure’ of the parent coal. In this respect the oxygen in the coal is considered to be of primary significance.     

Interactions between coking coals and plastics during co-pyrolysis☆

Blends of three Australian coking coals and polypropylene, polystyrene, polyacrylonitrile and polyphenylene sulfide were prepared and the extent to which the blends fused on heating was monitored using proton magnetic resonance thermal analysis in order to identify interactions between them that could affect their fluidity. Different plastics had different effects. Polystyrene strongly reduced the fluidity of all of the coals, confirming previous findings. Polypropylene did not affect the fluidity of the two coking coals of lower rank. Polyphenylene sulfide reduced the fluidity of the coals at temperatures near the solidification temperature of the coals, and polyacrylonitrile appeared to increase the fluidity of the coals at temperatures near the softening temperature of the coals. The very different effects different plastics have on coal fluidity show that the interaction between plastics and coals must be carefully examined before plastics are added to coking coal blends.     

基于PCR-多案例融合的焦化烟气脱硝过程指标优化设定

国内首座炼焦烟气脱硫脱硝一体化装置运行过程机理复杂、受上游焦化工况影响导致入口烟气指标频繁波动、且过程未知干扰严重,难以采用传统建立精确的数学模型进行过程指标设定值的求解。为了解决这一问题,提出了一种基于案例推理技术的焦化烟气脱硝过程指标优化设定方法。同时,由于焦炉换向操作的存在使相关特征描述值剧变,传统案例重用方法中采用单一特征描述当前工况极有可能导致结果存在偏差,针对这一问题,提出一种基于主成分回归多案例融合的案例检索与重用方法。通过进行仿真计算及实际工业应用,表明所提方法可以根据不同工况特征获得合适的操作参数设定值,有效地将出口NO_x浓度控制在工艺要求的区间内,并能极大地降低装置运行能耗。     

Calculating the relative value of coal in Russian coking-coal markets

In order to improve the pricing of Russian coking coal, a method is proposed for calculating the relative technological value of purchased coking-coal batches. The basic idea is to compare the parameters of optimal coking batch and coking batch that includes the purchased coking-coal concentrate and other coals available to a particular buyer. It is shown that the relative technological value of a particular batch of coking-coal concentrate will depend on the parameters of the other coals included in the coking batch at a particular coke plant.     

A physicochemical study of carbonization phases,Part II: quenching experiments at the pilot scale

Previous experiments carried out on several carbonization phases showed a relationship between tar migration and the coking pressure. In the present study, tests analogous in principle to the previous ones were conducted at a pilot scale with 400 kg coal charges. Two coals were used: C28, which leads to no pressure (“safe”), and C19, which induces pressure (“dangerous”). N-methyl-2-pyrrolidinone (NMP) extractions from the carbonization phases of the two coals confirm that tar migration is dependent on the nature of the parent coal, i.e. whether “safe” or “dangerous”. In the case of dangerous coal, the impregnation of non-coked coal by tars has been evidenced. In relation to this phenomenon, increased coking pressure is likely to develop due to the enrichment of non-transformed coal by volatile matter, as well as to the drop in permeability of this phase. It is also suggested that heavy tars clog up the pores of the semi-coke of dangerous coals.     

配合煤配比对焦炭综合热性质的影响

以企业生产实践为背景,研究在配合煤中增配肥煤和1/3焦煤对焦炭综合热性质的影响。对不同配比配合煤的性质指标进行检测,采用40 kg焦炉实施炼焦试验,并对炼制焦炭的传统国家标准热性质指标和利用自主研制装置测得的综合热性质指标进行测定。结果表明:增配肥煤和1/3焦煤,均会使配合煤的变质程度降低,挥发分含量升高,胶质体的黏结能力下降,但胶质体的量保持不变。配比变化引起的配合煤性质指标的变化没有显现在焦炭的传统国家标准热性质指标反应性CRI和反应后强度CSR上。以往的研究都是以CRI和CSR指标为目标量判断配合煤的配比是否合适,本研究除此之外还采用了自主提出的焦炭综合热性质指标。配合煤配比变化引起的焦炭的综合热性质指标变化比国家标准热性质CRI和CSR指标变化敏感,这可能与其反映了焦炭某些新的特征有关。基于焦炭综合热性质指标的变化规律,考虑到1/3焦煤具有经济性,生产上增配某些特定的1/3焦煤,可以同时达到提高焦炭质量和降低配煤成本的目的。     

Oil-cum-gas-fired experimental coke oven developed at CFRI and the correlation studies of its coke with commercial oven coke

Assessment of the coking behaviour of coals and blends by conducting coking tests in experimental coke ovens still continues to be the most reliable method and is extensively used all over the world. The oil-cum-gas fired experimental coke oven developed at CFRI has a coal charging capacity of 1100 kg and simulates industrial carbonising conditions. The oven is capable of intermittent operation and can be brought up to working temperature within 36 hours.Correlation studies of coke quality were carried out by conducting a series of coking tests on the same blend, carbonised under similar conditions in the CFRI experimental coke oven and the commercial coke ovens of Bokaro Steel Plant. The study has revealed that the physical strength of the CFRI oven coke compares favourably with the Bokaro oven coke. M₄₀ and M₁₀ indices of the commercial oven coke can be predicted fairly accurately from the results of CFRI oven coke.T-tests performed on the shatter results showed that at 5% probability level there was no significant variation between the shatter indices of both cokes. The quality of the gas produced from the CFRI test oven was very similar to that of the gas produced from the Bokaro ovens.     

Pitch and petroleum coke additions to coke oven charges

Several pitch materials and a petroleum coke were added to coke oven charges in an attempt to make good metallurgical coke from Canadian coal of poor coking quality. Coal and petroleum pitches were added to a low fluid western Canadian coal of medium volatile bituminous rank, and the blends coked in a technical-scale moveable wall test oven having a 230-kg charge capacity. Pitches improved coke tumble test indices, the principal coke quality parameter related to blast furnace performance. Varying levels of petroleum coke were added to an eastern Canadian coal of high volatile bituminous rank, and the blends, some partially briquetted, were carbonized in a test oven. Tumble indices of coke from the partially briquetted charges approached an acceptable level. These investigations confirm that petroleum products as well as coal derivative can play a useful part in the production of a metallurgical strength coke from poor or non-coking coals.     

焦炭光学组织在煤质鉴别中的应用

对我国山东、青海等地煤质较特殊的炼焦煤进行了工业分析指标、煤岩指标、焦炭光学组织和性能研究,并与同类型炼焦煤煤质进行比较。研究结果表明,焦炭光学组织能从本质上反映炼焦煤的质量,对一些煤质较特殊的煤,焦炭光学组织与工业分析指标和煤岩指标结合可更好地鉴别煤质。