Resumen de Captura de CO2 en centrales termoeléctricas mediante cocombustión de carbón y biomasa en condiciones de oxicombustión
[EN] Coal will continue to be one of the main energy resources for electricity generation in the future. However, coal combustion gives rise to CO2 which is a greenhouse gas and the main source of climate change. One alternative for the reduction of CO2 emissions is to replace part of the coal by biomass, whose emissions are considered neutral. However, to achieve any substantial reduction in CO2 emissions, additional measures must be taken, such as CO2 capture and storage technologies including oxy-fuel combustion. When fuel is burned in a mixture of pure O2 and recycled exhaust gases (i.e., in absence of N2) a highly concentrated stream of CO2 is produced, which after the purification process, can be transported to a place of storage. Oxy-combustion technology is at present in the demonstration phase. However, its economic viability will depend not only on technological advances but also on environmental policies. The performance of a wide range of coals and several biomasses under oxy-fuel combustion conditions has been studied. The replacement of N2 by CO2 and the higher O2 concentrations in oxy-fuel combustion atmospheres entails several changes in coal and biomass combustion that must be addressed in order to maintain stability and combustion efficiency. Various experimental devices have been used including a thermogravimetric analyzer, a drop tube furnace and an entrained flow reactor. Ignition and combustion under different oxy-fuel combustion conditions, and under air as reference, have been studied using these devices. Single coal and biomass particle combustion was studied in the drop tube furnace. Experiments were carried out under different oxy-fuel and air atmospheres. Measurements with a pyrometer were also carried out in the same furnace in order to obtain temperature profiles during the combustion of different single coal and biomass particles samples. In order to reproduce some of the conditions that are present in a pulverised coal fired power station, an entrained flow reactor was employed. Coal devolatilization at 1000 ºC, under N2 and CO2 atmospheres, was conducted in the entrained flow reactor. In order to study the effect of the devolatilization atmosphere (CO2, N2), the morphological characteristics of the chars were compared and their reactivity was analyzed. The reactive behaviour of the chars was studied by means of isothermal and non-isothermal reactivity experiments in an oxy-fuel atmosphere using a thermogravimetric analyser. Different kinetic models were applied to predict the reactivity of these fuels. Coal char and biomass char blends were analyzed in order to detect possible interactions during the combustion of the blends. Coal and biomass blend ignition tests were conducted in the entrained flow reactor under air and various oxy-fuel conditions at 1000 °C. Different oxy-fuel atmospheres were employed. Both oxy-fuel combustion with dry recycling (O2/CO2, 21-35%O2) and oxy-fuel combustion with wet recycling using up to 10 and 20% of H2O were simulated. The effect of biomass addition and the combustion atmosphere on the ignition temperature was evaluated. Co-firing experiments under oxy-fuel conditions were carried out in the thermogravimetric analyzer and in the entrained flow reactor. The coal and its blend with biomass were subjected to combustion experiments in the entrained flow reactor to evaluate the effect of the combustion atmospheres on coal burnout and NO emissions under oxy-fuel and air combustion.
