• Energy Research

Abstract The effects of coal preheating on the quality, textural and surface properties of the coke were assessed in comparison with the conventional wet charging system using a Spanish hvb coal. Coal was flash dried and preheated in a 2 t h− 1 Precarbon pilot plant. Carbonization tests on the wet and preheated coals were carried out in a semi-industrial scale oven of 6 tonne capacity. Because textural and surface properties have an important effect on coke quality, an exhaustive characterization of the resultant cokes was made. Cokes were characterized by using microscopic image analysis, mercury porosimetry, density measurements, optical and scanning electron microscopy (SEM) of surfaces. Mechanical strength and reactivity towards CO2 were also studied. Surface areas were determined by N2 adsorption at 77 K using the Brunauer-Emmett-Teller (BET) equation and CO2 adsorption at 273 K. using the Dubinin-Radushkevich (DR) equation. Coal preheating improved coke mechanical strength considerably but at the same time increased the reactivity of the cokes. The higher reactivity could be due to the increase in microporosity and CO2 surface area.

Biofuel pellets were prepared from biomass (pine, chestnut and eucalyptus sawdust, cellulose residue, coffee husks and grape waste) and from blends of biomass with two coals (bituminous and semianthracite). Their mechanical properties and combustion behaviour were studied by means of an abrasion index and thermogravimetric analysis (TGA), respectively, in order to select the best raw materials available in the area of study for pellet production. Chestnut and pine sawdust pellets exhibited the highest durability, whereas grape waste and coffee husks pellets were the least durable. Blends of pine sawdust with 10-30% chestnut sawdust were the best for pellet production. Blends of cellulose residue and coals (<20%) with chestnut and pine sawdusts did not decrease pellet durability. The biomass/biomass blends presented combustion profiles similar to those of the individual raw materials. The addition of coal to the biomass in low amounts did not affect the thermal characteristics of the blends.

The quest for green and effective synthetic routes towards energy grade materials is of utmost relevance in the transition to a fossil-free energy model. In a previous work we have shown the promising role of harmless MgSO4 in the synthesis of S-doped carbon anodes for fast sodium storage. Herein, we show that the same simple procedure can be used for the production of high surface, supercapacitor-type materials, by merely changing the temperature of the thermal treatment. We also found that the addition of an inert salt such as KCl -in small amounts- greatly boosts the porogenic activity of MgSO4, leading to carbons with SBET above 2000 m2 g−1. As a proof of concept, and using biomass-based substances as carbon precursors, we have built a hybrid sodium-ion capacitor out of a S-doped carbon and a highly porous carbon, both of them prepared using similar MgSO4-assisted synthetic schemes. The full cell built with similar positive and negative electrode masses exhibited a good energy/power performance (38Wh kg−1 at 22 kW kg−1), as well as a very robust cycling stability, with a capacity fade of only 0.00078 % cycle−1. This research work was supported by project IDI/2018/000148 (FICYT/FEDER) and PID2021-123648OB-I00 (MCIN/AEI/10.13039/501100011033/and ERDF A way of making Europe). S. Payá also thanks the Principality of Asturias for her Yo Investigo contract. Peer reviewed

Abstract Low-temperature pyrolysis by means of the Gray–King test was carried out with ten coals of different coking pressure characteristics. The final pyrolysis temperature was selected taking into account the beginning and end of the coking pressure development. The soluble fraction in dicloromethane obtained from the tars was analysed by gas chromatography using flame ionization detection (GC–FID) and high performance liquid chromatography (HPLC). The coking pressure generated by the coals was assessed by means of a movable wall oven. Furthermore, the contraction/expansion of the coals during thermal treatment was measured by using the Koppers-INCAR and sole heated oven tests. The primary tar composition was studied in relation with contraction/expansion and the coking pressure generated by the coals. Although not conclusive, there is strong evidence to suggest that the relative amount of heavy compounds in the primary tars is related to the coking pressure generated by the coals studied.

7 pages, 7 figures, 4 tables.-- Printed version published Sep 2008. Nine bituminous coals of different rank and geographical origin were carbonized at pilot scale coke oven (300 kg) in order to study the pressure generated during coking. At the same time their contraction/expansion was assessed by means of the Koppers-INCAR test. Semicokes were carefully recovered from the test so that their structure could be studied. The semicokes were separated into two parts, i.e. one that had been heated to 575°C and the other that had been heated to 700°C. The true and apparent density of the semicokes was measured together with their pore size distribution by means of mercury porosimetry and the results were related to the dangerousness of coals. The structure of the semicokes from safe and dangerous coals is different especially in those obtained at lower temperature. In addition, the fissures of the semicokes were evaluated. The area of the fissures was found to be greater in the case of non-dangerous coals. The authors thank the Ministerio de Ciencia y Tecnología –MCYT- (project PPQ2001-1450) and the European Coal and Steel Community-ECSC- (project 7220-PR/069) for the financial support provided. Peer reviewed

6 pages, 7 figures, 5 tables.-- Printed version published on Nov 3, 2008. The aim of the present work is to discuss the differences in the compositions of primary tars collected by means of Gray-King (GK) pyrolysis tests from coking coals of different origin and rank. Ten bituminous coals were pyrolyzed at two different temperatures, 450 and 550°C, which are known to be important in the conversion processes of coal. Low temperature tars were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Gas Chromatography (GC), Gas Chromatography-Mass Spectrometry (GC-MS), and High-Performance Liquid Chromatography (HPLC). The results indicate that low temperature tars are mainly formed by aromatic compounds containing different types of substituents (alkyl, aryl, heteroatomic and heterocyclic). When the coal rank increases, the amount of aliphatic and polar compounds decreases due to the influence of coal composition, while the amount of aromatic compounds such as naphthalenes, phenanthrenes, fluorenes, benzofluorenes, and their alkyl derivatives rises as a consequence of the increase in the aromaticity of the parent coal. The authors thank the European Coal and Steel Community — ECSC — (project 7220-PR/069) and Ministerio de Ciencia y Tecnología — MCYT — (project PPQ2001-1450) for financial support. Peer reviewed

The thermal characteristics and kinetics of coal, biomass (pine sawdust) and their blends were evaluated under combustion conditions using a non-isothermal thermogravimetric method (TGA). Biomass was blended with coal in the range of 5-80 wt.% to evaluate their co-combustion behaviour. No significant interactions were detected between the coal and biomass, since no deviations from their expected behaviour were observed in these experiments. Biomass combustion takes place in two steps: between 200 and 360 degrees C the volatiles are released and burned, and at 360-490 degrees C char combustion takes place. In contrast, coal is characterized by only one combustion stage at 315-615 degrees C. The coal/biomass blends presented three combustion steps, corresponding to the sum of the biomass and coal individual stages. Several solid-state mechanisms were tested by the Coats-Redfern method in order to find out the mechanisms responsible for the oxidation of the samples. The kinetic parameters were determined assuming single separate reactions for each stage of thermal conversion. The combustion process of coal consists of one reaction, whereas, in the case of the biomass and coal/biomass blends, this process consists of two or three independent reactions, respectively. The results showed that the chemical first order reaction is the most effective mechanism for the first step of biomass oxidation and for coal combustion. However, diffusion mechanisms were found to be responsible for the second step of biomass combustion.

Abstract Four coals that develop different pressures during the coking process were selected together with 10 blends (7 binary and 3 ternary) prepared with the same coals. Their semicoke contraction/expansion was measured by means of two tests (the Koppers-INCAR and the sole heated oven) and the variation in coking pressure during coking was determined in a movable wall oven. The coals and blends were then pyrolysed and the tars were analysed by gas chromatography (GC-FID–MS). The additivity law was applied to the properties used to evaluate the dangerousness of the blends and to the composition of the tar produced from the blends. Afterwards, the composition of the tar was studied in relation to contraction/expansion and the coking pressure generated by the coals and blends.