KINETIC STUDIES ON NUCLEAR-ASSISTED GASIFICATION OF ARGENTINE COALS

NASSINI H.; DE MICCO G.; FOUGA G. G.; BOHÉ A. E.

Praga

Workshop; IAEA´s Technical Meeting/Workshop on Non-Electric Applications of Nuclear Energy; 2011

IAEA - International Atomic Energy Agency

Coal gasification technologies offer the potential of clean and efficient energy. Nuclear coal gasification is a process that uses nuclear primary energy to convert coal into a synthesis gas for direct use, as well as for the production of hydrogen and liquid fuels that can be used economically under certain conditions, depending mainly on the location, the cost of coal, and the product and its price compared to natural gas and crude oil. In this context, Argentina is presently investigating the application of nuclear gasification technologies to a domestic low-rank coal extracted from the Río Turbio minefield, which is located in the southwest region of the country and represents, by far, the main national reserve of coal.For this purpose, a comprehensive research program is being implemented to characterize the behaviour of Río Turbio coal under typical gasification conditions with the objective of identifying the most suitable gasification process to be implemented for hydrogen production and liquid fuels production, respectively. The research program comprises both theoretical and experimental studies on laboratory scale which are designed to simulate the operational conditions of a large-scale gasification plant, and to provide the necessary information about the fundamental mechanisms and kinetics of gasification reactions.It is known that coal gasification is a two-step process. In the first step, pyrolysis, volatile components of coal are rapidly released at temperatures between 300 and 500 ºC, leaving residual char and mineral matter as byproducts. The second step, char conversion, involves the gasification of residual char that is much slower than the devolatilization step. In order to experimentally simulate the gasification conditions in a real gasifier and, then, achieve the kinetics/mechanism of the gasification, it is essential to reproduce, at least, (1) the rapid heating of coal particles, and (2) the gas convection around individual char particles with definable intensity. The experimental approach followed to achieve both objectives is the so-called two-stages experiments in which the gasification reactivities are determined on char samples prepared in a previous pyrolysis step, where coal particles are heated in a drop tube furnace at high-heating rates and short residence times.In this paper, results of kinetic studies on gasification of Río Turbio coal char in presence of steam and carbon dioxide (CO2) as gasifying agents, are presented. The kinetics of the CO2 gasification has been studied by thermogravimetry between 800 and 950 ºC and CO2 partial pressures from 28 to 82 kPa, using isothermal and non-isothermal measurements to study the influence on the reaction rates of several parameters such as the gaseous flow rate, sample mass, temperature, and CO2 partial pressure. It was observed that the gasification reactions start slowly at approximately 600 ºC and the reaction rate increases significantly at about 850 ºC. The experimental conditions under which the reaction rate is controlled by chemical reaction were established for the setup used, and a theoretical model to describe the evolution of the reaction degree as a function of time was developed.Steam gasification of Río Turbio coal char was also investigated using a specially designed experimental setup, able to produce different partial pressures of steam. Gasification reactions are produced in a tubular flow reactor heated by an electrical furnace that can reach temperatures up to 950 ºC. The overall reaction rates under different experimental conditions of gaseous flow rate and sample mass were determined by following the temporal evolution of the gaseous product concentration by gas chromatography.