The effects of using structurally less-stable raw materials for the support of a spray-dried oxygen carrier with high NiO content

• Published in: Fuel (Guildford) Vol. 102; pp. 106 - 114
• Main Authors: Baek, Jeom-In, Ryu, Chong Kul, Lee, Ji Hyun, Eom, Tae Hyoung, Lee, Joong Beom, Ryu, Ho-Jung, Ryu, Jungho, Yi, Jongheop
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-12-2012; Elsevier
• Subjects: Applied sciences; Chemical-looping combustion; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fuels; Nickel oxide; Oxygen carrier; Spray-drying method; Oxygen carrier; Chemical-looping combustion; Spray-drying method; Nickel oxide; Fluidized bed reactor; Gaseous fuel; Spherical shape; Thermogravimetry; Mechanical properties; Oxygen transfer; Raw materials; Oxygen content; Physical properties; Bubbling; Bentonite; Performance; Strength; Drying; Chemical looping combustion
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2012.05.049

► A spray-dried NiO oxygen carrier with excellent physical properties and reactivity was prepared. ► Mixture of structurally less-stable inorganic binders were used as raw materials for support. ► A calcination temperature to obtain sufficient mechanical strength was lowered to 1100°C. ► The performance of NiO oxygen carrier was remarkably improved.
An oxygen carrier for chemical looping combustion (CLC) requires high mechanical strength, high reactivity, and other physical properties suitable for fluidized-bed processes. Spray-dried NiO oxygen carriers prepared using structurally stable raw materials such as α-Al2O3 and MgAl2O4 as support have required a calcination temperature above 1400°C to obtain sufficient mechanical strength applicable to fluidized-bed process, and their oxygen transfer capacity has been less than 10wt%. Here, we present a spray-dried oxygen carrier prepared using high NiO content (70wt%) and structurally less-stable raw materials (20wt% γ-Al2O3, 5wt% pseudoboehmite, and 5wt% bentonite), which resulted in reducing a calcination temperature and enhancing the performances of the oxygen carrier. The prepared oxygen carrier showed excellent physical properties, especially high mechanical strength and spherical shape, suitable for fluidized-bed applications and high reactivity. The calcination temperature to obtain sufficient mechanical strength was lowered to 1100°C. At the reaction temperature of 950°C, the oxygen transfer capacities determined by a thermogravimetric analyzer were 13.9 and 12.4wt% for the oxygen carriers calcined at 1100 and 1250°C, respectively, indicating more than 82% of the total oxygen in the raw NiO was transferred to the fuel. The excellent physical properties were still maintained after ten cyclic redox tests in a bubbling fluidized-bed reactor. On the other hand, the oxygen carrier prepared with α-Al2O3 had sufficient mechanical strength when calcined at 1400°C, and showed much lower performance in reactivity and physical properties. This work confirms that the use of high NiO content and structurally less-stable raw support materials composed of γ-Al2O3 mixed with a small amount of pseudoboehmite and bentonite can reduce the calcination temperature to obtain sufficient mechanical strength and improve the performance of a spray-dried NiO oxygen carrier for the CLC of gaseous fuels.