Resumen de Eliminación de elementos metálicos tóxicos de los productos de gasificación del carbón
[EN] Coal contains elements, which can be potentially hazardous and corrosive. After coal gasification most of these elements may be found in gas phase in different proportions. In order to avoid the problems the presence of trace elements in the gas phase may originate during coal gasification processes a suitable technology needs to be developed. One possible option is the retention of the trace element in sorbents in the gasification plant. The systems currently being studied and developed for gas cleaning in coal gasification, focus on the removal of sulphur, particulate matter, nitrogen, alkali metals and halogens but not on corrosive and toxic trace elements. However, the reduction of trace elements using sorbents in gas phase at high temperatures appears to be a promising method in studies of combustion systems. The main objective of this project was to develop and ascertain the capability of different sorbents to retain trace element species in hot gases from gasification systems. The specific objectives were to determine how the operational variables and sorbent characteristics could influence trace element removal. To attain these objectives a theoretical study, based on thermodynamic equilibrium calculations, and an experimental study with a laboratory scale reactor were carried out. The reactor and the experimental conditions where the retention experiments were carried out were designed and set up specifically for the project. Different materials were tested as sorbents. These materials were characterised before and after the experiments by nitrogen adsorption, XRD, SEM-EDX and XPS. Retention capacity of each sorbent was determined by the analysis of the solid sorbent after the experiment by ICP-MS, ICP-MS/HG and AA/HG. Sorption experiments were carried out at different temperatures and gas atmospheres. The results obtained indicated that arsenic, selenium, cadmium, lead and cinc are present in gas phase during a coal gasification process. These species can be retained, totally or partially in solid sorbents at temperatures between 350 and 750ºC. The retention capacities and efficiency of the different sorbents for each element were determined in different conditions. In this work it was observed that, in a coal gasification atmosphere, limestone, fly ashes and metallic oxide mixtures containing spinels, were the best sorbents, though with each of them retention capacity depended on temperature and atmosphere. Probably, this retention takes place through different mechanisms, but in most of cases a chemical reaction occurs.
