Large-Scale Granulation of CaO-Based Pellets for High-Temperature Carbon Dioxide Capture

Abstract Pelletized CaO-based sorbents are made for the use in Moving Bed Carbonate Looping (MBCL) technology capturing CO2 at a low partial pressure of CO2 and high temperature, producing approximately 100% pure CO2. Developing this technology will be an important step in reducing CO2 emissions and prevent temperature increase on the globe. The main goal of this thesis was to develop a procedure for making these pellets in large scale. Material properties such as good CO2-capture capacity and stability, and good mechanical strength are important. A "rotary drum" granulation machine was used to produce granules made of 100g calcined dolomite/cement ADDA, calcium aluminate cement, extra magnesium and zirconium with water as a liquid binder. The preparation method lasted for two days due to the exothermic reaction between dolomite/ADDA and water, and water was slowly added to avoid early strength gain and increased hydration kinetics at higher temperatures. Six pellets based on calcined dolomite were made; NO-1 (pure dolomite), NO-3 (1.9% Zr from nitrates), NO-6 (1.6% Zr from ZrCl4 and 5.8%Al from cement), NO8 (2.9%Mg from magnesium nitrate and 5.5%Al (from cement)), NO-10 (6.1%Al from cement) and NO-12 (1.6% Zr from nitrates and 5.8%Al from cement). In addition, four pellets were made of cement ADDA. Results from nitrogen adsorption/desorption showed largest surface area for unpromoted pellets and smallest pores for the doped samples. Scanning electron microscope pictures, and mechanical tests seem to demonstrate good performance of pellets NO-3, NO-8 and NO-10. They have a similar pellet surface and sphericity, low cumulative attrition loss and weight loss in each drop in the falling test. The x-ray diffraction identified phases of mayenite (Ca12Al14O33), which might be the reasons for the excellent mechanical strength of NO-8 and NO-10. Results from sorption/desorption cycling in a thermogravimetric analyzer with 8% steam demonstrated promising CO2-carrying capacity and stability over 34 cycles for all pellets. Even though sample NO-1 has the worst stability, the stability was surprisingly high compared to other studies on powdered dolomite which have shown poor cyclic stability. The reason might be the preparation method and the raw material (calcined dolomite (3h 800◦C)