A novel air reactor concept for chemical looping combustion systems operated at high pressure

Abstract

We analyse the viability of a novel reactor concept for chemical looping combustion applications with CO2 capture. The reactor consists of a packed bed of reduced oxygen carrier particles traversed by a series of empty conducts oriented in the axial direction. These conducts are made of permeable but non-selective porous walls, through which air diffuses towards the region of reacting solids. The diffusion flux of air through the orifices, which is perpendicular to the main bulk flow of gas along the conducts, imposes very long oxidation times for all the reacting particles and a quasi-steady heating up of the air flow. The conducts designed to have a very high length/diameter ratio (i.e. above 50) allow a large bypass of pressurized air through the reactor without coming into direct contact with the solids, resulting in a modest pressure drop of the gas (i.e. below 5% at the reactor exit). A preliminary reactor design example is described for a case using Fe/Fe2O3 pellets as oxygen carrier, which are packed into a reactor (L = 100 m, I.D. = 2 m) traversed by air conducts (I.D. = 0.05 m) with a wall 2 mm thick and orifices occupying an area fraction of 0.12. The reactor can initially generate 100 MWth, with a gas flow at the exit at close to 1050 °C and 19 atm, and it could be used intermittently for more than 9 h as the main heater in a highly efficient Brayton cycle.