C. Barriocanal

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.

On the relationship between coal plasticity and thermogravimetric analysis

Abstract Two series of bituminous coals of different rank, geographic origin and plastic properties were subjected to thermal treatment up to 1000xa0°C in a nitrogen atmosphere at two heating rates (3 and 10xa0°C min −1 ), using two thermobalances of different design. Maximum fluidity of coal determined by the standardized Gieseler plastometry test was found to correlate well with the amount of volatile matter evolved up to 500xa0°C and with that evolved in the plastic or fluid stage (between 375 and 500xa0°C and 400 and 500xa0°C). In addition, a good linear relationship was found between the temperature of maximum evolution of volatile matter derived from the DTG curve and the characteristic temperatures indicating the beginning, end and maximum value of the fluid stage of coal. Although the experimental values of the parameters derived from thermogravimetric analysis are affected by the heating rate applied and the design of the apparatus, the correlations based on the results are little affected by the above variables.

A laboratory study of the mechanism of coking pressure generation

Abstract For a range of coals varying in the internal gas pressure they generated in a small oven, a small coking reactor was used to measure the volumes of gaseous volatiles which were released from the coal and coke exits of the reactor as the coals were carbonized. Simultaneous measurements were made of either the internal gas pressure or the pressure necessary to maintain a constant flow of nitrogen into the centre of the charge. Gases initial exited from the coke-side exit, but the direction of gas exit changed when the plastic layer neared the coal end of the charge, the effect being observed for all the coals examined. Internal gas pressures measured in the coking reactor placed the coals in the same order of pressure generated as the small oven. Nitrogen pressure peaks were generally higher than directly measured internal gas pressures and remained measurable to higher temperatures. The results are discussed with regard to the mechanism of coking pressure generation.

The laboratory identification of dangerously coking coals

Several coals, varying in the coking pressure they generate, were selected in order to study the coal properties influencing the escape of volatiles from carbonising coal charges. The aims of the work were to contribute to the understanding of the mechanism of internal gas pressure generation and to help identify dangerously coking coals. Volatile matter release rates from coal/sand mixtures and from packed coal beds were studied to assess whether gases could be trapped within fused coal beds. Also, the variation with temperature of the rate of volatile matter evolution and degree of Gieseler plasticity were compared to ascertain whether excessive pressures could be identified with high volatile release rates occurring when specific plastic properties were evident. It was found that the internal gas pressure generated by coals, when carbonised in a small double-wall oven, could be related to data obtained by plastometry and thermogravimetric analysis.

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.

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