Читать книгу Engineering Solutions for CO2 Conversion - Группа авторов - Страница 44

The application of strategies for capturing the CO₂ from combustion processes is of great importance for effectively implementing CO₂ conversion approaches and thus reducing the impact of industrial activity regarding CO₂ emissions. Oxyfuel technology is one of the most considered options for conducting the implementation of this capture and sequestration of CO₂ from exhaust gases, as well as for improving the efficiency of the aforementioned industrial processes [31–33]. The oxyfuel approach applied to combustion processes consists of burning the fuel with a pure or O₂‐rich stream, thus obtaining mainly CO₂ and H₂O as products. Consequently, CO₂ sequestration can be easily carried out with a simple separation step.

Nevertheless, oxyfuel technology is still far from being implemented in the most of targeted industrial processes. The main reason is related to the O₂ supply, which is not economically feasible for those applications. Currently, almost all the O₂ is produced by cryogenic distillation of air. This process, which is operated at very low temperatures and high pressures, requires from high energy and large production plants that avert its consideration for O₂ on‐site production in small‐ and medium‐scale installations. An appealing solution for implementing an O₂ supply system in such applications can be performed by considering oxygen transport membranes (OTMs). OTMs are ceramic membranes consisting of metallic oxides with the ability of diffusing O²⁻ ions through the oxygen vacancies present in their crystal lattice. This is due to the mixed ionic–electronic conductivity (MIEC) of these materials at high temperatures (>600 °C), thus allowing O₂ separation with 100% selectivity from a high pO₂ feed stream (pressurized air) to a low pO₂ sweep stream (vacuum or recirculated flue gas stream). Furthermore, waste heat streams generated in high‐temperature processes in several industries requiring from O₂ supply for conducting combustions (e.g. cement plants, ceramic and glass production, and power plants) can be used for heating the OTM modules up to their operating temperature. This thermal integration can then result in a significant increase in plant efficiency and in a reduction in O₂ production costs, which can be lowered up to 35% with respect to conventional cryogenic distillation [34].