Marian san Pio Bordejé (PhD)
Unraveling the origin of the redox kinetics behavior of oxygen carriers in chemical looping combustion
With Chemical-Looping Combustion (CLC) CO2 capture is integrated with power production with minimal energy penalty, since the CO2 capture is intrinsic to the reaction system. In CLC oxygen is transferred from the combustion to air to the gaseous fuel by means of solid oxygen carriers particles. The fuel and the combustion air are never in direct contact, and the gases from the fuel combustion leave the system as a separate CO2 rich stream. It has been found that the reaction rate dramatically changes at different stages of oxidation and reduction, causing simple phenomenological models often used in literature to fall in predicting the behaviour of the oxygen carriers. There is thus an intrinsic difficulty in designing and optimizing CLC reactors.
The concept of CLC is depicted in Figure 1. Previously, the research on CLC has been focussed predominantly on the use of a dual circulating fluidized bed system, where the oxygen carrier material is transported between two fluidized bed reactors (the air and the fuel reactor).
The research and development has recently led to a next generation of the CLC technology, which can maximize the benefits of the principle behind CLC while reducing the complexity of the process and costs. This new concept developed by our research group uses dynamically operated packed bed reactors, which offer a cost effective solution with significant advantages with respect to operation at elevated pressures and scaling up abilities (Norman et al., 2007, 2011).
The objective of this research is to elucidate the origin of the redox kinetics behaviour of oxygen carriers in chemical looping combustion via a combined experimental and computational study. State-of-the-art experimental techniques (high pressure and high temperature TGA and magnetic suspension balances in combination with detailed characterization techniques) will be used to monitor for the first time the morphological and chemical changes that particles undergo during the oxidation and reduction cycles in combination with their reduction and oxidation kinetics. A novel computational model will be developed and experimentally validated that quantitatively describes the redox kinetics of oxygen carriers. The particle model will be integrated inside packed bed reactor models to quantify the effects of morphological changes of the oxygen carrier particles on the operation of packed bed CLC reactors. With the advanced reactor model, a system integration and energy analysis of the entire packed bed CLC system will be carried out.
In Figure 2, are shown the typical particle conversion profiles and the comparison of TGA measurement results and model predictions. At any rate, different models for gas-solid reactions have been developed in literature to predict the time dependence of the conversion of oxygen–carrier particles and the effect of the operating conditions on the reaction rates.
This project started in August 2013 and will be develop in the next four years until 2017. The main objective will be integrated in a developed and advanced particle model into a reactor model for packed bed CLC in order to determine how morphological changes of the oxygen carrier particles affect the operation of packed bed CLC reactors.
This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organization for Scientific Research (NWO), and which is partly funded by the Ministry of Economic Affairs.