M.D. Casal

Mechanical durability and combustion characteristics of pellets from biomass blends.

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.

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.

Modifications of coking coal and metallurgical coke properties induced by coal weathering

Chemical changes in the structure of organic matter of coking coals during storage modify their thermoplastic properties and behaviour during carbonization. As a result, the anisotropic carbon structure of the metallurgical cokes produced and their physical properties are altered. In this work, the weathering behaviour of 10 bituminous coals of different geographic origin, rank and thermoplastic properties, used as components in the preparation of industrial coking blends for coke manufacture, was studied by means of Gieseler plastometry and Fourier transform infrared (FTIR) spectroscopy. These coking coals were stored in piles at the Instituto Nacional del Carbon (INCAR) open stockyard for a period of time of up to 7 months. Special attention was paid to the relationship between the relative amount and type of aliphatic hydrogen (semi-quantitatively evaluated by FTIR), and thermoplastic properties. Depending on the nature of the coking coal, a different response to natural weathering can be expected. Thus, the results showed that there is a direct link between a decrease in methylene groups and a loss of fluidity in the weathered coals, resulting in a decrease in anisotropic carbon of the resultant cokes with weathering time. In addition, the rate of anisotropic carbon loss induced by weathering could be associated with the rank parameters of the initial coals.