CaCO3 calcination by the simultaneous reduction of CuO in a Ca/Cu chemical looping process

Abstract

The exothermic reduction of CuO to Cu using a fuel gas as a source of heat to carry out the simultaneous calcination of CaCO3 in a fixed bed is evaluated. The absence of apparent large energy penalties, as in other chemical looping processes, is an indication that there is great potential for achieving a high level of energy efficiency with this Ca/Cu looping concept. A dynamic pseudo-homogeneous model has been developed to describe in detail the transient behavior of this operation in a fixed-bed reactor under adiabatic conditions. A sensitivity analysis of the main operating parameters (i.e. the CuO/CaCO3 molar ratio, starting temperature and fuel gas composition) confirms the theoretical viability of this operation. A balanced CuO/CaCO3 ratio ensures a suitable bed performance allowing the reduction and calcination fronts to advance together, reach moderate maximum temperatures of around 900°C and leave behind totally converted solids. The use of CO as fuel gas significantly reduces the CuO/CaCO3 ratio required for the CaCO3 calcination. A careful adjustment to bed composition must be carried out, since an excess of CuO in the bed will generate more heat than required for the calcination, and consequently hot spots higher than 1000°C will form along the bed. In contrast, an excess of CaCO3 will increase the energy demand and part of the bed will be left uncalcined.