Small scale fluidized bed experiments under oxygen combustion conditions

In oxygen combustion fuel is burned with almost pure oxygen and recycled flue gas without nitrogen from the air. By avoiding the diluting effect of nitrogen, the carbon dioxide capture of flue gas becomes more effective. Gas atmosphere in the reactor depends on flue gas recirculation ratio and consists mainly on carbon dioxide, water vapour and oxygen. Gas atmosphere has effects on burning rate, reaction kinetics, emission formation and sulphur capture by limestone. VTT (Technical Research Centre of Finland) has in Jyvaeskylae unique small scale fluidized bed combustors applicable for oxygen combustion research. Pilot scale (30-100 kW) circulating fluidized bed (CFB) reactor can be operated at air firing and at oxygen combustion mode. Reactor is equipped with O{sub 2} and CO{sub 2} feed from gas tanks and also with flue gas recirculation for demonstrating real oxygen combustion conditions. In addition, a smaller BFB/CFB reactor {lt} 1 kW), which can be operated at batch and continuous combustion modes, is suitable for phenomena studies of oxygen combustion. A set of oxygen combustion experiments with bituminous coal and limestone feed was carried out with pilot and laboratory scale reactors. With CFB-pilot reactor, normal air combustion is compared to oxygen combustion with O{sub 2}/CO{sub 2} feed from gas tanks and to real oxygen combustion with flue gas recirculation. Fuel reactivity and limestone sulphur capture tests were carried out at varying oxygen combustion conditions with laboratory scale reactor, and results were compared to air combustion. At pilot tests, feed gas oxygen content varied between 21-40% and at laboratory scale tests between 5-50%.