R. Alvarez

Coal for metallurgical coke production: predictions of coke quality and future requirements for cokemaking

This paper reviews quality requirements of metallurgical coke for the blast furnace, coke structure, and relationships between structure and quality. Models of prediction of metallurgical coke quality parameters based on maceral composition and properties of coals being carbonized are summarized. Early prediction models of cold coke strength and the development of second-generation hot-strength prediction models based on parameters as coke reactivity index (CRI) and coke strength after reaction with carbon dioxide (CSR) are assessed. The review concludes with an assessment of current coke production and coal demand in the steelmaking industry, globally, followed by a preview of possible future alternative coking technologies.

Pyrolysis of a waste from the grinding of scrap tyres

The fibres that are used to reinforce tyres can be recovered as a waste in the process of grinding of scrap tyres. In this paper beneficiation through pyrolysis is studied since the fibres are made up of polymers with a small amount of rubber because the latter is difficult to separate. The experiments were performed at three temperatures (400, 550 and 900°C) in a horizontal oven. The three products - gas, oil and char - obtained from the pyrolysis were investigated. The composition of the gas was analyzed by means of gas chromatography. The oil was studied by gas chromatography and infrared spectroscopy. The char porous structure was determined by N(2) adsorption. In addition, the topography of the chars was studied by means of scanning electron microscopy (SEM). The products resulting from the pyrolysis of the fibres were compared with those obtained from scrap rubber.

Gas chromatographic study of the volatile products from co-pyrolysis of coal and polyethylene wastes.

The aim of this study was to determine the volatile products distribution of co-processing of coal with two plastic wastes, low-density polyethylene from agriculture greenhouses and high-density polyethylene from domestic uses, in order to explain the observed decrease in coal fluidity caused by polyethylene waste addition. Polymeric materials, although they are not volatile themselves, may be analysed by gas chromatography through the use of pyrolysis experiments. In this way, a series of pyrolysis tests were performed at 400 and 500 degrees C in a Gray-King oven with each of the two plastic wastes, one high-volatile bituminous coal and blends made up of coal and plastic waste (9:1, w/w, ratio). The pyrolysis temperatures, 400 and 500 degrees C, were selected on the basis of the beginning and the end of the coal plastic stage. The organic products evolved from the oven were collected, dissolved in pyridine and analysed by capillary gas chromatography using a flame ionization detector. The analysis of the primary tars indicated that the amount of n-alkanes is always higher than that of n-alkenes and the formation of the alkenes is favoured by increasing the pyrolysis temperature. However, this effect may be influenced by the size of the hydrocarbon. Thus, the fraction C17-C31 showed a higher increase of n-alkenes/n-alkanes ratio than other fractions. On the other hand, the difference between the experimental and estimated values from tars produced from single components was positive for n-alkanes and n-alkenes, indicating that co-pyrolysis of the two materials enhanced the chemical reactivity during pyrolysis and produced a higher conversion than that from individual components.

Determination of metallurgical coke reactivity at INCAR: NSC and ECE-INCAR reactivity tests

AbstractCertain aspects of the Nippon Steel Corp. (NSC) based test for measuring metallurgical coke reactivity were studied at the Spanish National Coal Institute (INCAR). It was found that some highly reactive cokes do not follow the correlation between the coke reactivity index (CRI) and the coke strength after reaction (CSR) observed in most metallurgical cokes. It was proved that the temperature of the furnace at the beginning of the NSC test is irrelevant to the subsequent determination of CRI and CSR. By starting the test with a hot furnace, the total operation time and energy consumption can be reduced. In addition, a good correlation was found between the NSC test and a simpler and more economical test: the ECE-INCAR reactivity test.

Modification of coking behaviour of coal blends by plasticizing additives

Abstract Commercial coal-tar pitch (CTP) and pitch-like residue (RP)—a waste by-product of coking plants—were used as an additive to two coal blends in metallurgical coke production. The additives were characterized in terms of chemical composition, solvent analysis, 1 H NMR spectroscopy, extrographic fractionation, hydrogen transfer properties, thermogravimetric analysis and plastic properties. Both the thermal behaviour and hydrogen transfer properties of the additives are crucial for the coal plastic phase modification during co-carbonization. CTP improves the coking properties of coal blend, i.e. coking and swelling abilities, dilation and fluidity, whereas RP leads only to a fluidity enhancement. This is reflected in different yields, anisotropic carbon, microstrength and reactivity to carbon dioxide of the cokes produced at two different laboratory scales. The beneficial effect of the additives on the metallurgical coke quality not only depends on the properties of the additives themselves, but also the coking properties of the coal blend to which the plasticizing agent was added is a critical factor.

Gas chromatographic study for the evaluation of the suitability of bituminous waste material as an additive for coke production

Abstract Waste materials derived from coking plants can be used in situ as bituminous additives in cokemaking. The effectiveness of such materials in the plastic coal range was compared with a coal-tar and four derived pitches of different applications. The volatile matter released from 400 up to 500°C by the additives (VM400–500), which was evaluated by thermogravimetric analysis, was clearly related to the extent of the modification of the Gieseler maximum fluidity of coking coal/additive blends. The decrease in the amount of volatile fraction in the CS 2 extracts of the additives and the increase in the abundance of polycyclic aromatic hydrocarbons (PAHs) of relatively high molecular mass were evaluated by capillary gas chromatography with flame ionization detection (GC–FID) analysis. From regression analysis, it can be deduced that there is a relationship between the compositional parameters deduced from GC–FID analysis and the volatile matter released in the plastic range of a coking coal (VM400–500). Both composition and VM400–500 of the additive, were found to be responsible for the enhancement in fluidity caused by the presence of the additive in the co-carbonization system. GC–FID analysis may be a good method to assess the effectiveness of a bituminous additive in the coal plastic stage and to acquire a better understanding of the components involved in this critical stage of the carbonization process. The changes induced in the plastic range by the additive modify the development of coke anisotropy and the bonding between coke matrix and inert material and, consequently, are responsible for the improvement in the coke properties.

Photoacoustic FT-IR study of weathered stockpiled coking coals

Abstract The process of weathering (natural oxidation) of two medium volatile bituminous coking coals stored at the INCAR open stockyard for several months has been studied by means of Gieseler plastometry, the free-swelling index (FSI) test, and by photoacoustic Fourier transform infrared spectroscopy (PA-FT-IR), the latter technique allowing only the surface of the sample exposed to the atmosphere to be analyzed. The proximate and ultimate analysis of the coals did not reveal any significant changes in their chemical composition. The Gieseler maximum fluidity (MF), however, was found to decrease with weathering time; using PA-FT-IR, a reduction in the aliphatic hydrogen content and a shortening of the alkyl chains was also detected. In addition, changes in the proportion of the oxygen-containing structures were observed, although the evolution of this kind of groups with weathering time was dependent on the raw coal.

Relation between texture and reactivity in metallurgical cokes obtained from coal using petroleum coke as additive

A laboratory-scale study was performed in order to investigate the effects that the addition of petroleum coke has on the texture and reactivity of the resultant metallurgical cokes. It was observed that the addition of petroleum coke to coking blends causes a reduction in the micropore volume and reactivity of metallurgical cokes. A relation between these two parameters was found, suggesting that the decrease in reactivity is a consequence of the decrease in surface area undergone by the metallurgical cokes obtained with petroleum coke addition.

Hydrogen donor and acceptor abilities of pitches from coal and petroleum evaluated by gas chromatography

Abstract Among the characteristics of coal-tar and petroleum pitches, the thermal reactivity of their constituents is one of the most important because it determines the development of mesophase and, consequently, the structure of graphitizable carbons (cokes). At the early stages of the carbonization process the hydrogen transfer reactions and the availability of donatable hydrogen are crucial to give high fluidity/low viscosity systems. In such conditions, aromatic molecular systems have enough mobility to stack parallel to each other resulting in a more ordered coke structure. A chemical procedure for estimating the reactivity of a pitch to supply and consume hydrogen from the reaction system is the co-carbonization with anthracene and 9,10-dihydroanthracene (DHA) as hydrogen acceptor and donor agents, respectively. A series of pitches including impregnation and binder coal-tar pitches, petroleum pitches and pitch-like residues from the by-products coking plants was studied. Carbon disulphide extracts from the co-carbonization systems (pitch+anthracene and pitch+DHA) were analyzed by capillary gas chromatography. Results indicate that pitches with the highest hydrogen donor ability favour the formation of 1,2,3,4-tetrahydroanthracene in the reaction system. The relation between the amount of volatile matter released in the temperature range of 400–500°C and the hydrogen donor and acceptor ability of the pitches can be considered as important factors in the development of coke structure.

A semi-industrial scale study of petroleum coke as an additive in cokemaking

Abstract The addition of petroleum coke to a typical industrial coal blend used in the production of metallurgical coke was studied. Cokes were produced at semi-industrial scale at the INCAR coking plant, using petroleum coke of different particle size distribution as an additive. Special attention was paid to changes caused in the textural properties (porosity, pore size distribution, fissures at the interface between metallurgical coke and petroleum coke) which have been found to be responsible for variations in the metallurgical coke quality parameters (e.g., mechanical strength and reactivity towards CO 2 ). Variation in porosity was found to depend on particle size and the proportion of the additive. The decrease in the microporosity (i.e., pore radius